Step 1: Preheat your oven to 350°F (175°C).
Step 2: In a large mixing bowl, melt the 1 cup of unsalted butter and let it cool slightly.
Step 3: Add the 2 cups of packed dark brown sugar, 2 lightly beaten eggs, and 1 tablespoon of vanilla extract; stir until well combined.
Step 4: Add 2 cups of all-purpose flour, 3/4 teaspoon of baking powder, 1/2 teaspoon of baking soda, and 1/2 teaspoon of salt to the bowl; stir gently until just combined.
Step 5: Fold in the 1 cup of chocolate chips and 1 cup of toffee pieces.
Step 6: Grease your 9x13 inch baking pan or line it with parchment paper. Pour the batter into the pan and spread it out evenly.
Step 7: Lightly sprinkle flaked sea salt over the top of the batter.
Step 8: Bake for 20-25 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.
Step 9: Let the blondies cool in the pan for about 10 minutes, then transfer to a wire rack to cool completely before cutting into squares.
