01 -
Turn your oven to 350 Fahrenheit (175 Celsius). Line a muffin tin with paper liners so cookies don’t stick and are easy to pull out.
02 -
In a large bowl, beat the butter and sugars until it's nice and fluffy. Add the egg if you’re using it along with vanilla, then mix well. Slowly fold in the flour until you get a dough.
03 -
Mix the peanut butter and powdered sugar in another bowl until smooth. Roll into 24 to 30 little balls. Chill them in the fridge for about 10 minutes so they firm up.
04 -
Press dough into each lined muffin cup, making a small dip in the middle. Pop a peanut butter ball inside each. Sprinkle chocolate chips and extras on top and cover with some dough.
05 -
Brush the tops with the egg yolk mixture to make them golden and glossy once baked.
06 -
Bake for 12 to 15 minutes until edges turn lightly golden and centers look set but still soft.
07 -
Let them rest in the pan for five minutes. Then, move the bites to a wire rack. The peanut butter will be warm and melty now, but it firms up as it cools.