1. Prepare the Crust:

1. Preheat oven to 350°F (175°C). Grease and flour a 9-inch round cake pan.
2. In a large bowl, cream together butter and sugar until light and fluffy. Beat in eggs one at a time, then stir in vanilla.
3. In a separate bowl, whisk together flour, baking powder, and salt. Gradually mix into the butter mixture, alternating with the heavy cream.
4. Pour half the batter into the prepared pan. Sprinkle with half the cinnamon. Add remaining batter, then swirl remaining cinnamon through the top with a knife.
5. Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean. Cool in pan for 10 minutes before transferring to a wire rack.