Place the softened butter, sweetener, protein powder and vanilla in a large bowl and use a hand mixer to combine until smooth. Taste and adjust sweetness to your liking. Place the mixture into a mini silicone muffin pan (or the bottom of a parchment lined 8x8 inch baking dish). Place in the fridge while you make the chocolate coating.
To make the chocolate coating, place the chopped chocolate and butter into a medium bowl. Heat in the microwave at 20 second increments and stirring in between until the chocolate is completely melted. Add the sweetener and prime protein. Use a hand mixer to combine until smooth. Taste and adjust sweetness to your liking. Pour over the peanut butter layer. Place in fridge for 4 hours to set.
Store extras in an airtight container in the fridge for up to 7 days. Can be frozen for up to a month.