Preheat oven to 350 degrees. Line a 12 cup muffin tin with liners.
In a large bowl, sift flour, cocoa powder, sugar, baking soda and salt together. Set aside.
In a large measuring cup mix buttermilk, oil, and vanilla. Pour buttermilk mixture into the flour mixture, and mix until everything is well combined. Fold in the Nestlé® Toll House® Dark Chocolate Morsels. Using an ice cream scoop (about ¼ cup), fill each muffin tin to ¾ full.
Bake for 15-20 minutes, until a tester comes out clean. Remove from oven, and turn onto a wire rack to cool completely.
Meanwhile prepare the filling. In a large bowl mix together the powdered sugar, milk, and both the extracts. It will be slightly thinner than frosting.
In the bowl of an electric mixer, cream together the butter and melted Nestle Toll House Dark Chocolate Morsels. Add sugar, milk, and vanilla. Beat until light and fluffy. You can add more milk or sugar to get your desired consistency.
Once the cupcakes have completely cooled, scoop 1 teaspoon of cake out of the center. Pour in some of the mint filing. Top with frosting.