Preheat oven to 350
Generously grease the inside rings of a doughnut baking pan with butter or shortening to prevent sticking
In a large bowl, combine 3 Tbs melted butter with ¾ cup brown sugar until thoroughly mixed
Stir in egg and vanilla
Add heavy whipping cream, flour and baking powder and stir until well combined
Transfer batter into piping bag and pipe one layer of batter into each doughnut hole in the baking pan
Bake for 15 minutes, or until a toothpick inserted into the middle of a doughnut comes out clean
Allow to set on a wire rack to cool completely before adding caramel glaze