Brown Sugar Butterscotch Cupcakes

and 2/3 cup (210g) all-purpose flour (careful not to overmeasure)

baking powder

baking soda

salt

packed light brown sugar (or dark brown)

or 115g) unsalted butter, melted

large egg, at room temperature

yogurt*

milk*

vanilla extract

or 230g) unsalted butter, softened to room temperature

(360-480g) powdered (confectioners') sugar

heavy cream*

and 1/2 teaspoons vanilla extract

salt, as needed