INGREDIENTS
1
and 3/4 cups (220g) all-purpose flour (or more as needed, see note)*
1/2 tsp
baking powder
1/4 tsp
baking soda
1/4 tsp
salt
10 tbsp
unsalted butter, softened to room temperature
1 cup
granulated sugar
1
large egg, at room temperature
2 tsp
pure vanilla extract
1/3 cup
full-fat sour cream, at room temperature*
5
and 1/2 cups (660g) confectioners' sugar, sifted (measure before sifting)
7 tbsp
whole milk, divided
2 tbsp
light corn syrup
1 tsp
pure vanilla extract
1/2 tsp
salt
3 tbsp
unsweetened natural or dutch-process cocoa powder*