Butterscotch Cupcakes Supreme

INGREDIENTS

1/4 cup

dark brown sugar

1/4 cup

water

2 tsp

white or dark rum

1/4 cup

unsalted butter

1 cup

packed light or dark brown sugar

3/4 cup

whipping cream (35%)

2 tsp

pure vanilla extract

1/2 tsp

sea salt or fleur de sel

1 3/4 cups

all-purpose flour, sifted

1/2 cup

cake flour, sifted

1 cup

packed dark brown sugar

2 1/2 tsp

baking powder

1/2 tsp

salt

1 cup

unsalted butter, cold and cut into small even pieces

2/3 cup

milk, at room temperature

2 tsp

pure vanilla extract

1 tsp

lemon juice

eggs, at room temperature

1 cup

whipping cream (35%), cold

3/4 cup

confectioners' sugar

1 cup

mascarpone cheese, softened

Toffee bits for sprinkling