The original recipe called for sugar, which is 50 percent glucose and 50 percent fructose, but I substituted dextrose (a powdered form of glucose) because a growing body of research indicates that eating fructose causes major health issues. If you’re a fructose malabsorber, fructose can cause other problems as well.
While this recipe is definitely an indulgence, it uses a lot less sweetener than many buttercream recipes. A number of recipes I looked at used up to 4 cups of powdered sugar. Corn syrup, liquid glucose, is what makes this recipe succeed, so don’t substitute something else for it. Read the labels carefully to make sure you’re buying pure corn syrup and not a brand mixed with high fructose corn syrup. Manufacturers sometimes mix the two products.
Feel free to substitute any liqueur for the Kahlua. While Kahlua does have some sugar in it, I only used two tablespoons, so the amount of fructose in it is minimal. Or try the lemon or chocolate variations. I buy large organic eggs, which tend to have smaller yolks than regular large eggs, so I weigh the yolks to make sure that I use the correct amount. I highly recommend that you weigh things- it’s the most accurate way to measure ingredients and there are fewer dishes to wash.
Kahlua Buttercream Frosting
Adapted from “The Cake Bible”
Enough frosting for two 8 inch cake layers and 12 cupcakes, two 9 x 1 1/2 inch cake layers, or three 9 x 1 inch cake layers
112 grams egg yolks, room temperature (6 to 7 large egg yolks)
150 grams dextrose (1 cup + 2 tablespoons)
164 grams corn syrup (1/2 cup)
454 grams (1 pound) unsalted butter, room temperature
2 tablespoons (30 ml) Kahlua or other flavoring variation
Grease a 1-cup (240 ml) heatproof glass measuring cup. Place it next to the stove. Use either a stand mixer or a hand-held mixer. Put the egg yolks into a large bowl and beat them until frothy. Combine the dextrose and corn syrup in a small pan and heat on medium-high. The mixture will be stiff, so stir constantly, until the dextrose dissolves and the mixture comes to a full, roiling boil with bubbles across the entire surface. The finished buttercream will be thin if the syrup doesn’t come to a full boil. Pour the syrup into the glass measuring cup to stop the cooking.
Pour a tiny bit of the syrup into the yolks and beat for 5 seconds. Turn off the mixer and add a little bit more syrup, then beat on high for another 5 seconds. Repeat this process until all of the syrup is mixed into the yolks. Continue mixing until the yolk mixture is cool, about 10 minutes. It’s very important that the mixture is completely cooled or it will be too thin after the butter is beaten in. Use a rubber spatula to scrape the sides of the bowl.
With the mixer running, add small chunks of butter one at a time. Wait for each chunk to be incorporated before adding the next one. When all of the butter is mixed in, add the Kahlua or other flavoring and mix thoroughly. The buttercream will last for 6 hours at room temperature. If you are not frosting your cake immediately, transfer the buttercream to a bowl, cover it tightly, and store it in the refrigerator for up to a week. The buttercream can be frozen for up to 8 months. Bring it to room temperature before using. If needed, use a mixer to beat it again to restore the texture. Don’t beat cold buttercream or it will curdle.
Lemon Buttercream Variation:
1/4 cup (60 ml) freshly squeezed lemon juice
1/4 teaspoon (1.25 ml) lemon extract
Pour the lemon juice into a small, non-reactive saucepan and bring to a boil over high heat. Stir constantly, until the juice is reduced by half. Let cool and add it, along with the lemon extract to the finished buttercream, beating until completely mixed in.
Chocolate Buttercream Variation
30 grams (1/3 cup) cocoa powder
70 grams (1/2 cup) dextrose
56 grams (1/4 cup) coconut oil or non-hydrogenated organic shortening
2 tablespoons (30 ml) Kahlua, optional
Melt the oil or shortening in a bowl and mix in the cocoa and dextrose until blended. Set aside to cool. Add the chocolate mixture to the buttercream and mix until thoroughly combined. Taste and add the extra Kahlua if you want. There will be the faintest hint of coconut if you use coconut oil, but it adds a subtle touch to the taste.
June 7, 2013: Cocoa powder recently tested moderately high in FODMAPs at the Monash University lab, which means the chocolate version below may no longer be considered suitable for a low-FODMAP diet. Here’s a link to what dietician Patsy Catsos has to say on the topic: http://www.ibsfree.net/ibsfree_at_last/2013/06/cocoa-powder-moderately-high-in-fodmaps-what-about-chocolate.html