Preheat oven to 425°F. Lightly grease doughnut pan; set aside.

In a medium bowl, add all of the dry ingredients (cake flour, granulated sugar, baking powder and salt). Stir until well mixed.

In a separate bowl, whisk together the egg, milk, vanilla extract, melted butter and heavy cream.

Add the liquid ingredients to the dry ingredients; stir until just mixed.

Spoon or pipe the batter into the greased doughnut pan. (Tip: Fill each doughnut circle about half full of batter.)

Bake at 425°F for 12-14 minutes, or until doughnuts begin to turn golden brown on the edges.

Let doughnuts cool in the pan.

Place powdered sugar in paper bag. Once doughnuts have cooled, shake doughnuts (one at a time) in the bag with the powdered sugar until well coated. Tap off any excess powdered sugar. Repeat with remaining doughnuts. Serve immediately. (Note: If you plan on serving these doughnuts later, store them uncoated in an air-tight container. Shake them in powdered sugar just before serving.)