Preheat the oven to 350°F and line an 8x8-inch baking pan with parchment paper, leaving overhang on two sides.
Whisk together the almond flour, coconut flour, erythritol, baking powder and salt. Add the melted butter, egg and vanilla and stir into a thick, soft dough.
Press the dough evenly into the pan with damp fingers, pushing it slightly up the sides. Bake for 8 minutes, then reduce the oven to 325°F.
Beat the cream cheese until completely smooth. Beat in the allulose and melted butter, then the eggs one at a time and the vanilla, mixing just until combined.
Pour the topping over the warm base. Bake for 30 to 35 minutes, until the edges are golden and set but the center still has a slight wobble. That wobble is what keeps the middle gooey, so do not overbake.
Cool completely in the pan, then chill for 1 hour for clean slices.
Dust with powdered erythritol and slice into 16 bars.