Homemade Thin Mints (Girl Scout Copycat!)

Ingredients

• 2 cups all purpose flour, spooned and leveled
• 2/3 cup dutch process unsweetened cocoa
• 2 tsp. cornstarch
• 1 tsp. baking powder
• 3/4 tsp. kosher salt
• 1 cup unsalted butter, softened
• 1 cup granulated sugar
• 1/2 cup dark brown sugar, packed
• 1 large egg, room temperature
• 1 large egg yolk, room temperature
• 1 tsp. vanilla
• 3/4 - 1 tsp. peppermint extract (not mint extract) (use less or more depending on how peppermint-y you want your cookies)
• 20 oz. dark chocolate melting wafers (you can also use high quality semi sweet chocolate but I like how the wafers set up.)
• 1 tsp. oil (canola or vegetable)
• 1/2-1 tsp. peppermint extract (use less or more depending on how peppermint-y you want your cookies)