• Preheat oven to 350F (175C) and prepare two 24-cavity mini muffin tins by spraying with baking spray or lightly greasing and flouring.
  
• Combine melted (cooled) butter and sugars in a large bowl, stir well.
  
• Add eggs, and egg yolk one at a time, stirring well after each addition.
  
• Stir in vanilla extract.
  
• In a separate, medium-sized bowl, whisk together flour, cornstarch, baking powder, and salt.  
  
• Gradually stir dry ingredients into wet until completely combined. Stir in chocolate chips.
  
• Use a 1 ½ Tbsp-sized cookie scoop to drop batter into prepared muffin tin wells.
• Bake on 350F (175C) for 18 minutes or edges are just beginning to turn golden brown.
  
• Allow cookie cups to cool for 5 minutes, and then use a rounded teaspoon to press into the center of each brownie bite and create a well (press a little more than halfway into each cookie).
  
• Allow brownie bites to cool another 10-15 minutes in the muffin tins, and then gently remove to cooling rack to cool completely.  Prepare your ganache.
  

Ganache

• Combine chocolate chips, heavy cream, and butter in a small saucepan over medium-heat.
  
• Stir frequently until chocolate is completely melted and mixture is smooth.
• Remove from heat and stir in vanilla extract, bourbon (if using), and salt. Stir well.
• Allow mixture to cool slightly at room temperature, about 10 minutes.
  
• Use a small spoon to pour ganache into the indent of each brownie.
• Allow ganache to firm up before eating (about 1-2 hours -- or you can enjoy them warm, it'll just be a bit messier).