Melt the chocolate chips and butter over low heat on the stove or microwave for 1-2 minutes and stir until completely smooth. Set aside.
Preheat oven to 350 degrees F.
Add the oil, eggs, yolk, vanilla extract, stevia and cream to a stand mixer and mix until combined.
Slowly pour in the melted chocolate while the mixer is on low speed.
Add the remaining ingredients and blend until combined.
Line an 8 by 8 pan with parchment paper or grease pan.
Pour half the batter in pan, then the peanut butter filling then remaining batter. Bake for 25 minutes. It might look underdone but it's best to take it out before it looks done to achieve that gooey texture.
Allow to cool 15 minutes before slicing.
Best if enjoyed the same day although storing in the fridge, covered, will keep well for the 2-3 days.