Below is our recipe for blackberry buttercream, the one my daughter mounded atop our white cupcakes and decorated with fresh berries and mint leaves. Julia Child’s Italian Meringue from The Way To Cook (a thorough, beloved, yet challenging encyclopedia of good cooking) is my usual starting point (and also ending point for some cakes if we just want a marshmallow-y “boiled icing”, like this double chocolate cake), but I also adapted ideas from Nancy Kux’s Classic Meringue Buttercream from the Baker’s Dozen Cookbook. I enjoy experimenting with adding jams and fruit syrups for part of the sugar to introduce natural fruit flavors and colors to buttercream.
To make the blackberry syrup, I thawed frozen blackberries in the refrigerator, then strained the berries from the juice to make a compote. I didn’t want to toss the juice, so I boiled with equal parts sugar, as if I was making a simple syrup, like this recipe, only no hot chile peppers!
- 2/3 cup sugar
- ¼ cup water
- 4 egg whites, room temperature
- ½ tsp. cream of tartar
- a pinch of salt
- 3 Tbsp. homemade blackberry syrup (start with equal parts juice, either strained from thawed whole berries or juiced from fresh fruit and strained from seeds, and sugar)
- 3 sticks unsalted butter (12 ounces), room temperature
- Whisk egg whites until foamy, using whisk attachment on a stand mixer.
- Sprinkle in the cream of tartar and a pinch of salt, then gradually increase speed to high and whisk until egg whites hold soft peaks. Turn the speed to low as you make the sugar syrup.
- Combine the sugar and water in a small saucepan and set on the stovetop over medium heat. Bring to boil and cook, without stirring, until sugar is dissolved and temperature reaches soft-ball stage on a candy thermometer (225 degrees F at 5000ft. elevation). Add the blackberry syrup and bring back to boil.
- Drizzle the boiling sugar syrup into the egg whites, increase mixer speed to medium, and beat until cool and egg whites form "stiff, shining, upstanding peaks" (thanks Julia Child!)
- Now it's time to add the butter, one tablespoon at a time, while keeping the mixer on medium speed and beating after each addition until it is absorbed into the meringue. Use to frost cupcakes same day, or refrigerate for up to 1 week. Freeze buttercream, or any leftovers, in a freezer bag for up to 3 months.
Amy’s Kitchen Coach Tips
- Don’t throw out leftover buttercream. Put it in a ziplock freezer bag, date it with a Sharpie, and freeze it. To bring it back to life, ideally thaw the bag overnight in the refrigerator. If you’re in a rush, you can microwave on defrost power (usually 30%) until it is slightly softened. Put the thawed buttercream in your stand mixer with the whisk attachment and turn it on. If it is still too cold to revive itself, you can either set the mixing bowl over a pan of hot water until about one quarter of the buttercream is melted, or you can remove one quarter of the total amount, melt it in the microwave, then drizzle it into the more firm buttercream. Beat, beat, beat. It’s a play between butter that’s too cold and too soft. Relax and you will restore the frozen lump of buttercream to its original consistency in no time. If you get things too runny, place the bowl in the refrigerator for 15 minutes and beat again.
- To make strawberry buttercream, I’ve cut the sugar in half and added an equal amount of homemade strawberry jam with good results. Add the jam to the sugar syrup after it has reached softball stage, stir to combine, and bring back to boil before drizzling into the meringue.