1 1/2 cups (330 grams) firmly packed light brown sugar3/4 cup (170 grams) unsalted butter, melted2 large (100 grams) eggs, room temperature1 teaspoon (4 grams) Heilala Gingerbread Vanilla Extract1 1/2 cups (188 grams) all-purpose flour1 teaspoon (5 grams) baking powder1 teaspoon (3 grams) kosher salt3/4 teaspoon (1.5 grams) ground ginger3/4 teaspoon (1.5 grams) ground cinnamon1/2 teaspoon (1 gram) ground nutmeg1/4 teaspoon ground cloves4 ounces (113 grams) white chocolate, roughly choppedVanilla Bean Buttercream (recipe follows)Garnish: assorted holiday sprinkles
Preheat oven to 350°F (180°C). Spray a 9-inch square baking pan with cooking spray. Line pan with parchment paper, letting excess extend over sides of pan.
In a large bowl, whisk together brown sugar and melted butter until smooth and well combined; whisk in eggs and gingerbread vanilla extract.
In a medium bowl, whisk together flour, baking powder, salt, ginger, cinnamon, nutmeg, and cloves. Stir flour mixture into butter mixture just until dry ingredients are moistened. Fold in white chocolate. Using an offset spatula, spread batter into prepared pan.
Bake until golden brown and a wooden pick inserted in center comes out with a few moist crumbs, 25 to 35 minutes. Let cool completely in pan on a wire rack.
Using excess parchment as handles, remove from pan. Cut into 3 (9×3-inch) strips. Cut each strip into 7 (2-inch-wide) triangles.
Transfer Vanilla Bean Buttercream to a pastry bag fitted with a small closed star piping tip (Ateco #842), and pipe onto blondies. Garish with sprinkles, if desired. Store in an airtight container for up to 3 days.