There is a magical time that comes but once a year, when a jolly old soul delivers special treats to all the good little boys and girls around the world. Or at least the United States, Canada, and Ireland. No silly, I’m not talking about Santa Claus delivering toys, I’m talking about Uncle O’Grimacey delivering McDonald’s Shamrock Shakes. I don’t know what it’s like in Canada or Ireland, but here in America, as soon as February rolls around, people start searching the internet to discover when they can get their sweet, green milkshake fix.
For those of you who aren’t familiar, or haven’t put two and two together yet, a Shamrock Shake is a minty vanilla milkshake McDonald’s puts out for a limited time each year to celebrate St. Patrick’s Day, (Oh, and Uncle O’Grimacey is Grimace’s green, furry Irish Uncle created to market said milkshake). If you haven’t had the distinct pleasure of sampling this nectar of the St. Patrick’s Day gods, then you are missing out. Shamrock Shakes are a delight. So much so, that I decided I had to try to put that deliciousness into a cake.
First off, I’ll give you the low down on how I went about getting the flavor profile. The Shamrock Shake is mint flavored, but the mint is not overpowering. It’s definitely an equal blend of vanilla and mint, so I wanted to be careful about how much mint I used. I decided to stick with a vanilla cake, and used my go-to from Liv for Cake. I wanted to infuse a simple syrup with mint as well, but needed it to be subtle, so I took a handful of fresh mint, crushed it a bit in my hands, and then tossed it in with the water and sugar while making the simple syrup. I use a base recipe for simple syrup you can find here. After finishing the syrup, I added a dash of vanilla extract as well, to try to maintain that balance.
After brushing the vanilla mint simple syrup onto my cake layers, I used a peppermint white chocolate ganache to fill them. To make the ganache, I heated 5 ounces of cream over low heat until it was steaming (stir as you heat), then I poured it over 10 ounces of white chocolate chips in a heat-safe bowl, let it sit for about five minutes, then whisked until all the chips were melted. If it doesn’t melt the whole way you may need to pop it in the microwave and heat at half power for 10-15 seconds at a time, whisking in between, until you get it completely smooth. For the peppermint flavor, I used peppermint oil from LorAnn. This was my first time using peppermint oil instead of peppermint extract, and I knew the flavor was much more concentrated so I was a bit cautious about adding it. I dropped from the bottle into a spoon first, to avoid pouring too much at once, then poured a drop at a time from the spoon. I stirred thoroughly and tasted in between additions until I got a flavor that was enough, without being too much. Very Goldilocks and the Three Bears. I would love to give you an exact amount, but I lost count, and everyone’s drops are likely to be different sizes (plus everyone has different tastes), so I’m not sure giving you a specific number would help anyway. I believe I used around 7 drops. I would just do the same thing I did, and taste as you go.
To give a counterbalance to the peppermint ganache, and sort of mimic the whipped cream on the top of the Shamrock Shake, I made a vanilla Ermine buttercream. Ermine buttercream is made by cooking a sort of pudding made out of flour, sugar, and milk, cooling it down, and then beating it into some butter. I find the taste very similar to whipped cream; light, fluffy, and not too sweet. I’m still trying to find the perfect Ermine recipe. This time I went with one from The Tough Cookie. It had a good stable texture and piped better than others I’ve tried (Ermine buttercream tends to be a bit softer), but the taste was much more buttery to me. Once it was balanced with the sweeter ganache, though, I appreciated it.
I think the combination of the vanilla cake, vanilla mint simple syrup, peppermint white chocolate ganache, and vanilla Ermine buttercream really nailed the taste of the Shamrock Shake, but I also wanted the cake to look like a Shamrock Shake. I baked my cake in four 4 inch round cake pans, then split each one into two layers. I only used 4 layers for this cake, so I’ve got some in my freezer for a rainy day. Once I stacked, filled, and crumb coated my cake with the ganache, I let it sit in the refrigerator overnight to firm up. The next morning, I tried my hand at cake carving. I’ll preface this by saying, I have never carved a cake before. I am no expert, but I’ll share my technique with you anyway. I used a serrated knife and my cake turntable, and slowly worked my way around the cake, basically shaving off the outer edges at an angle. I wanted the base of the cake to be smaller than the top, just like a cup is.
I worked VERY slowly, and took off only a tiny bit at a time, because you can always take off more, but you can’t really put any back. I also knew I’d have to stop myself at some point, or I would obsess over slight differences from one side to another. I would have liked to have carved it a little narrower, so the proportions would be more accurate, but I felt like I was losing too much cake. I wanted it to look good, but I still wanted a decent amount of cake on there, so I had to settle for a cup that was a bit wider and squatter than the real deal.
After I was semi-satisfied with the shape, I tinted about half of my buttercream mint green and put that in a piping bag. Then I took a little less than half of the white buttercream that was left and put that in a piping bag as well. I did not use piping tips for these, just snipped off the tips of the bags and used them to pipe frosting onto the cake. A Shamrock Shake has a bit of a swirly mix of white and mint green, so I piped green around and up the cake, leaving some gaps here and there. Then I filled in with the white. You don’t really want stripes here, so you have to make sure you’re breaking up your rounds a bit.
After piping the buttercream on the sides, I used a bench scraper to slowly smooth out the sides. I had to play with this a little as I went. Anytime it was looking too stripey, I used the bench scraper or a knife to smear the two colors together a bit more, then started smoothing again.
Once I was happy with the sides of the cake, I smoothed the top edge over the top of the cake, and got ready to finish it off with my “whipped cream” swirl. I took an ice cream scoop and scooped some of the remaining white buttercream on top of the cake and created a bit of a mound, smoothing it out with an offset spatula.
I did this so I could get some height to my whipped cream topping without having to pipe a lot in the middle. Then, using a 1M piping tip, I filled a bag with the rest of the buttercream, and piped around the mound I had made until I got to the top.
I wiggled the bag a little as I piped to create a ruffled look, like what you would get from a can of whipped cream. Last but not least, I plopped a maraschino cherry on top, and stuck a McDonald’s straw in at a jaunty angle.
It was so much fun to recreate this super cool treat and I think Uncle O’Grimacey would approve. Let me know what you think of this cake, or just of Shamrock Shakes in general, in the comments. Share that Shamrock love!