Part 1: Preparation

1. Preheat Oven and Prepare Pan: Position a rack in the middle of your oven and preheat to 350°F (175°C).

2. Line the Pan: Line an 8×8 inch (20×20 cm) square baking pan with parchment paper, ensuring there is a 2-inch overhang on two opposite sides. This creates a “sling” which will allow you to easily lift the blondies out of the pan for slicing once they have cooled.

Part 2: Mixing the One-Bowl Batter

1. Combine Wet Ingredients: In a large mixing bowl, combine the melted butter and the packed light brown sugar. Whisk them together until the mixture is smooth and well combined.

2. Add Egg and Vanilla: Add the room temperature egg and the vanilla extract to the butter and sugar mixture. Whisk vigorously for about 30 seconds until the batter becomes lighter in color and slightly glossy. This step helps create the desirable crackly top.

3. Add Dry Ingredients: Add the blanched almond flour, baking powder, and fine sea salt directly into the same bowl. Switch to a rubber spatula and stir until the dry ingredients are just incorporated. Do not overmix. The batter will be thick and shiny.

4. Fold in Chocolate Chips: Reserve about 1/4 cup of the chocolate chips for the topping. Gently fold the remaining 3/4 cup of chocolate chips into the batter.

Part 3: Baking and Cooling

1. Spread in Pan: Scrape the thick batter into your prepared baking pan. Use the spatula to spread it into an even layer, pushing it into the corners.

2. Add Toppings: Sprinkle the reserved 1/4 cup of chocolate chips evenly over the top of the batter. Finish with a generous sprinkle of flaky sea salt.

3. Bake: Place the pan in the preheated oven and bake for 20-25 minutes. The blondies are done when the edges are set and golden brown, and the center is no longer wet but is still soft. A toothpick inserted into the center should come out with moist, fudgy crumbs attached, not wet batter.

4. Cool Completely (Crucial Step!): Remove the pan from the oven and place it on a wire rack. You must let the blondies cool completely in the pan for at least 2 hours. They will be very soft and delicate when they first come out of the oven and will firm up significantly as they cool. Attempting to slice them while warm will result in a crumbly mess.

Part 4: Slicing and Serving

1. Lift and Slice: Once completely cool, use the parchment paper sling to lift the entire blondie slab out of the pan and onto a cutting board.

2. Cut into Squares: Use a large, sharp knife to cut the slab into 16 squares. Serve and enjoy!