Heat the oven to 350°F and line an 8-inch square pan with parchment paper. Stir the peanut butter, powdered allulose, melted butter, and vanilla together until smooth.
Whisk the almond flour, cocoa powder, allulose, baking powder, and salt together in a large bowl.
Whisk the eggs, melted butter, melted sugar-free chocolate, and vanilla together. Stir the wet mixture into the dry ingredients just until a glossy batter forms.
Spread half of the brownie batter in the pan. Drop the peanut butter mixture over it in small spoonfuls, leaving a little brownie batter visible between the mounds.
Spoon the remaining brownie batter over the top and gently spread it to cover most of the peanut butter without fully mixing the layers.
Bake for 22 to 26 minutes, until the edges are set and the center is still slightly soft. Cool for 20 minutes for a molten peanut butter center, or cool completely for fudgier slices.
Lift from the pan and cut into squares, wiping the serving spatula between cuts for clean layers.