1Combine filling ingredients (1/2 cup unsalted butter, melted; 2/3 cup dark brown sugar; 1 tbsp ground cinnamon) and set aside to firm up (or chill for 10 minutes).
2Combine wet ingredients (1 1/2 cup unsalted butter, room temp; 1 1/2 cup granulated sugar; 2 eggs; 1 tbsp vanilla; 1/3 cup heavy cream) until light and fluffy.
3Add dry ingredients (2 tsp baking powder; 1/2 tsp baking soda; 1 tsp salt; 4 1/2 cup + 1 tbsp AP flour) little by little and combine.
4Coat a large piece of parchment paper with flour and flatten the dough into a large rectangle.
5Spread the filling all over the dough, leaving an inch around the edges.
6Roll the dough up and chill for 30 minutes.
7Slice the chilled dough log into 14 portions and roll into balls. Chill the dough balls in the freezer for 30 minutes.
8Bake on 350 for 14 minutes. Use a spatula to fix the cookies if they spread too much.
9Combine icing ingredients (3 tbsp butter, melted; 1 3/4 cup powdered sugar; 2-3 tbsp milk) and drizzle over cooled cookies.