- Grease the pan. For easy removal of the bars, place parchment paper on the bottom and 2 sides of the pan. Grease again and then set aside. Preheat oven to 350°F. Melt the butter and set aside as you prep the rest of the ingredients. 
- In a large bowl, add melted and cooled butter, brown sugar, and white sugar. Whisk until well combined. - 3/4 cups butter, 3/4 cups light brown sugar, 1/4 cup white sugar 
- Add in egg, yolk, and vanilla. Continue whisking. - 1 egg, 1 egg yolk, 1 tbsp vanilla 
- Add in the flour, baking powder, and salt. Using a rubber spatula, gently fold it in until a soft batter forms. It will be runny. - 2 cups all-purpose flour, 1/2 tsp baking powder, 1/2 tsp salt 
- Toss in the semi-sweet and mini chocolate chips and mix in a few times. - 1/2 cup semi-sweet chocolate chips, 1/2 cup mini chocolate chips 
- Pour into the prepared pan and spread out evenly. Top with extra chocolate. 
- Bake for 22-25 minutes or until the blondies are a light golden colour. The bars continue to bake as they cool in the hot pan, so it's okay if they're underbaked when removed from the oven. 
- Let the cookie bars cool completely before slicing, and enjoy! I personally love to have them with a scoop of vanilla ice cream.