Prepare the Brownie Layer:
Preheat oven to 325°F (163°C). Grease a 9-inch springform pan.
In a large bowl, mix melted butter, granulated sugar, cocoa powder, and salt until combined. Cool slightly if warm.
Stir in vanilla extract and eggs one at a time, then fold in flour just until combined. Pour into prepared pan.
Bake for 15 minutes. Cool completely, then chill in the fridge while preparing the cheesecake layer.
Make the Cheesecake Layer:
Beat cream cheese until smooth. Gradually add granulated and brown sugars, then cream, mixing until well combined. Scrape down the sides of the bowl.
Add eggs one at a time, mixing just until incorporated after each addition. Blend in vanilla.
Pour over chilled brownie base. Tap pan on counter to release air bubbles.
Bake and Cool:
Place springform on a rimmed baking sheet. Bake at 325°F for about 55 minutes to 1 hour, or until set but slightly wobbly in the center.
Turn off oven, crack oven door open, and let cheesecake cool in oven for 10 minutes to prevent cracking.
Remove from oven, cool to room temperature on a wire rack, then refrigerate for at least 4 hours, or overnight.
Finish and Serve:
Release cheesecake from pan. Drizzle with additional caramel sauce and, if desired, garnish with whipped cream and chocolate shavings.
Slice and serve chilled.