Strawberry Rhubarb Swiss Meringue Buttercream
(Adapted from Martha)
4 large egg whites
1 1/4 cups sugar
1 1/4 cups unsalted butter, room temperature, cut into tablespoons
1 teaspoon pure vanilla extract
1 cup Rhubarb Preserves
1/2 Cup Puréed Strawberries
In the heatproof bowl, either of an electric mixer or you can transfer it after, set over a saucepan of simmering water, combine egg whites and sugar. Cook, whisking constantly, until sugar has dissolved and mixture is warm to the touch (about 160 degrees). I have never been able to get mine to 160. I usually top out about 145º. I also wouldn't whisk this by hand if you don't have to. Your arm will be sore. I used my little hand beater and it still took about 10 minutes to get to 145º and fluffy.
Transfer or Attach the bowl to the mixer fitted with the whisk attachment. Beat the egg-white mixture on high speed until it holds stiff (but not dry) peaks. Continue beating until the mixture is fluffy and cooled, about 6 minutes.
This is where it starts to get a bit tricky, I was really lucky this time as it came together great.
Switch to the paddle attachment. With mixer on medium-low speed, add butter several tablespoons at a time, beating on medium high after each addition. Do not add more butter until the all incorporated (If frosting appears to separate after all the butter has been added, beat on medium-high speed until smooth again, 3 to 5 minutes more.) Beat in vanilla. Beat on lowest speed to eliminate any air bubbles, about 2 minutes or stir with a spatula by hand.
Stir in jam and purée with a rubber spatula until frosting is smooth, mine looked a little curdled after this part so I put the bowl back on the mixer and mixed with the whip attachment for about a minute on medium high and it came back together. If you have more problems, this link should help you out!
I piped these pretty high, I had 18 cupcakes and still had enough to pipe them all this high and cover half an Angel Food Cake (which I had left over, delicious). I used my large star tip (1M) piped the bottom layer and then did the extra swirl on the top.