In a medium sauce pan, melt butter over medium heat. Stirring often, allow to cook 2-3 minutes, until butter smells nutty. Remove from heat and allow to cool completely (30 minutes).
Once butter has cooled, preheat oven to 350°. Line an 8x8 baking pan with parchment paper. Set aside.
In a large mixing bowl, combine butter, brown sugar and granulated sugar. Beat with an electric mixer until smooth.
Add eggs to butter mixture, beat with an electric mixer for 1 minute until smooth and well combined.
Add vanilla extract and beat until combined.
In a separate mixing bowl, sift flour and baking powder. Add flour mixture to batter and mix until combined.
Fold chocolate chips into batter.
Spoon dough into prepared baking pan, spreading dough evenly. Bake for 30 minutes.
Remove baking pan from oven, sprinkle chopped milk chocolate bar evenly onto blondie. Bake an additional 2-3 minutes.
Remove from oven and sprinkle with sea salt flakes. Allow to cool completely. Cut into squares. Store up to 5 days in an airtight container.