<p>To prepare the lemon sugar topping:</p><p>In a small bowl, mix the sugar and zest; use your fingertips to rub the zest into the sugar until the mixture is fragrant. Set aside.</p><p>To prepare the blondies:</p><p>In a large bowl, whisk together the melted butter, demerara sugar, powdered sugar, and salt until smooth and glossy.</p><p>Add the egg, egg yolk, lemon extract, and zest, then whisk until well combined. Add the flour, baking soda, and mix with a spatula to form a thick batter.</p><p>Pour the batter into a gn 1/2 prepared with a sheet of parchment paper and spread it into an even layer using the spatula or your hands. Sprinkle with the lemon sugar topping.</p><p>Place in the oven.</p><p>Let cool and unmold.</p><p>Dust with powdered sugar and cut into square pieces.</p>