Preheat the oven to 350°F and line an 8x8-inch baking pan with parchment paper, leaving overhang on two sides.
In a large bowl, whisk the melted butter and granulated sweetener together. Add the eggs and vanilla and whisk for 1 minute until glossy.
Add the almond flour, cocoa powder, baking powder and salt. Stir until a thick, smooth brownie batter forms. Set aside 1/4 cup of the batter, then spread the rest evenly in the pan.
In a separate bowl, beat the cream cheese and powdered sweetener until smooth. Add the pumpkin puree, egg yolk, pumpkin pie spice and vanilla and beat until creamy with no lumps.
Spread the pumpkin mixture over the brownie layer. Drop small spoonfuls of the reserved brownie batter on top, then drag a toothpick or skewer through both layers to create swirls.
Bake for 28 to 32 minutes, until the edges are set and the center has only a slight jiggle. Do not overbake, as the brownies firm up while cooling.
Cool completely in the pan, then chill for at least 1 hour. Lift out using the parchment and slice into 16 squares.