Preheat the oven to 3250F and line an 8x8 inch metal baking pan with parchment paper.

In a large microwave-safe bowl, melt the peanut butter and butter together until smooth.

In a separate bowl, whisk together almond flour, sweetener, collagen powder, baking powder, and salt. Combine with the melted peanut butter mixture, egg, egg yolk, and vanilla extract.

Press two-thirds of the dough into the prepared pan. Sprinkle with marshmallows and gently press.

Crumble the remaining dough over the marshmallows. Bake for 20 to 25 minutes until lightly browned.

Let cool completely before lifting from the pan and cutting into squares.