In a microwavable mug mix the butter and sugars together.
Add egg yolk and peanut butter and continue mixing.
Stir in flour, then mix until all ingredients are fully combined.
Microwave for 40-60 seconds (check after 40 seconds to check if it is done, you might have to play around with the timing as all microwaves are different)
IMPORTANT NOTE:My microwave is 1200Watts and my cookie took 40-45 seconds. Don’t overcook or they can dry out. Mug cookies are best eaten while still warm.
Top off your mug cookie with a buttercream frosting mixed with raspberry jam.