Preheat the oven to 350ºF, grease an 8x8-inch baking dish and line it with parchment paper. Set aside.
Melt the butter and when it is warm, stir in the eggs, allulose, cocoa powder, vanilla, and salt.
Add the almond flour, lupin flour, and gelatin and stir until evenly blended.
Pour into the lined pan and bake for 15-20 minutes, or until the middle is just set. Better to undertake than over-bake for a chewy and slightly gooey brownie.