-
1
Preheat oven to 350. Line a muffin tin with paper liners.
-
2
In a small bowl, mix together flour, baking powder, and salt.
-
3
In a large bowl, whisk together sugar, butter, and egg until smooth. Add yogurt, lemon zest, lemon juice, and lemon extract. Beat until smooth. Add flour and mix just until smooth.
-
4
Scoop batter into paper liners. Bake 22-25 minutes. Let cool in pan for 10 minutes. Remove from pan and let cool completely on rack before frosting.
-
5
For frosting:
-
6
Wash and hull strawberries. Puree in food processor and set aside.
-
7
Add sugar and egg whites into bowl of mixer. Fit over pan of simmering water. Whisk constantly, keeping mixture over heat, until it feels hot to the touch, about 3 minutes.
-
8
Remove bowl from heat. Using the whisk attachment on a stand mixer, beat meringue on medium speed until cool, about 5 minutes.
-
9
Switch to paddle attachment and add butter, one tablespoon at a time, beating until smooth. Once all the butter is in, beat on medium-high until very smooth and thick, 6-10 minutes. If the buttercream curdles or separates, keep beating and it will come together again.
-
10
Gradually beat in lemon juice, then the vanilla. You should have a shiny, smooth, velvety white buttercream. For lemon buttercream, stop at this point. For strawberry-lemon buttercream, add the strawberry puree.
