Preheat the oven to 350F (180C) degrees.
Line the bottom of a 9-inch springform pan with parchment paper and lightly spray the sides with non-stick cooking spray. Alternatively, lightly spray a 9-inch pie plate with non-stick cooking spray.
In a large bowl, beat together the butter, brown sugar and white sugar until fluffy.
Mix in the peanut butter until smooth.
Then mix in the egg, additional egg yolk and vanilla extract.
With the mixer on a low speed, beat in the flour, baking powder and salt until combined.
Stir in the chocolate chips and Reese's Pieces (or whatever mix-ins you're using).
Spoon the cookie dough into the prepared pan and flatten down into an even layer.
Bake in the preheated oven for about 24-28 minutes, or until the top is golden.
Remove from the oven and cool fully if you're adding frosting on top.