Preheat the oven to 375F and grease 3 small ramekins. Dust the ramekins with cocoa powder and shake out the excess.
In a microwave safe bowl, melt the butter and chocolate together, whisking until smooth. Alternatively, you can melt it carefully in a pan over low heat.
Add the sweetener and whisk until combined. Then add the egg and egg yolk and whisk until smooth. Whisk in the almond flour, vanilla extract, and salt until well combined.
Divide about two thirds of the batter between the three ramekins, making sure to cover the bottoms.
Divide the peanut butter between the ramekins, placing in the center of the batter. Cover with the remaining batter and spread to the edges.
Bake 10 to 12 minutes, or until the edges of the cakes are set but the center still jiggles slightly. Remove and let cool 5 to 10 minutes. Then run a sharp knife around the edges and flip out onto plates.