1/2 cup packed light brown sugar
4 tablespoons (1/2 stick) unsalted butter
1/4 cup heavy cream
1 teaspoon vanilla extract
In a saucepan over medium heat bring the brown sugar, butter, and cream to a boil. Reduce heat to a simmer (about medium-low) and continue stirring for 5 minutes. Remove from heat.
Stir in the vanilla.
Pour the warm caramel topping over cupcakes. (***I HIGHLY ADVISE LETTING THE CARAMEL COOL AND THICKEN BEFORE TOPPING THE CUPCAKES!!*** Otherwise you'll just get a thin, runny mess and hardly any caramel on each cupcake. I let mine cool in the refrigerator for about 10 minutes, stirring every few minutes.)
(I had to double this recipe to cover all 16 cupcakes.)