To make the cupcakes
Divide the batter evenly between the prepared cupcake liners. Bake for 18-20 minutes, until a toothpick inserted in the center comes out clean. Allow to cool in the pan 5-10 minutes, then transfer to a wire rack to cool completely.
To make the cookie dough filling
Combine the butter and sugar in a mixing bowl and cream on medium-high speed until light and fluffy, about 2 minutes. Beat in the flour, sweetened condensed milk and vanilla until incorporated and smooth.
To make the frosting, beat together the butter and brown sugar in the bowl of a stand mixer fitted with the paddle attachment until creamy. Mix in the confectioners’ sugar until smooth. Beat in the flour and salt. Mix in the milk and vanilla extract until smooth and well blended.
For the cupcakes:
For the filling:
For the frosting: