Cream butter and sugar for 2-3 minutes on medium high with paddle attachment.
Mix egg and vanilla in separate bowl. Add egg and vanilla to butter/sugar and cream for 7-9 minutes.
Portion bite size pieces using cookie scoop, roll into balls and place on parchment lined cookie sheet.
Smoosh them down a bit and using a powdered sugar covered finger, indent to make the "thumbprint." Set aside.
Melt peanut butter then add powdered sugar until combined.
Spoon melted peanut butter mixture into "thumbprint."
Chill on pan in fridge for at least one hour.
Once ready to cook, bake at 375 F for 9-11 minutes.
While cookies are cooling, prepare your chocolate drizzle.
Set up a double boiler (metal bowl over a boiling pot of water) and add chocolate chips. Using a rubber spatula, stir your chocolate chips to melt and then add 1/2 cup of milk. Let it combine and melt completely until desired consistency. You may need to add more milk to get it thin enough.
Use a fork and drizzle melted chocolate over your thumbprint cookies.
Let cool and serve with coffee or hot chocolate!