Preheat oven to 350°F (180°C). Line an 8-inch square baking pan with parchment paper, letting excess extend over sides of pan.

For blondies: In a large bowl, whisk together brown sugar, salt, baking powder, and ½ teaspoon (1 gram) nutmeg. Gradually add melted butter, whisking just until combined. Whisk in brandy and vanilla extract. Add eggs, one at a time, whisking until combined after each addition. Stir in flour until just combined. Spread batter into prepared pan.

In a small bowl, whisk together granulated sugar and remaining ⅛ teaspoon nutmeg; sprinkle onto batter.

Bake until a wooden pick inserted in center comes out with just a few moist crumbs, 25 to 30 minutes. Let cool completely in pan on a wire rack.

For glaze: In another small bowl, whisk together confectioners’sugar, milk, reserved vanilla seeds, and nutmeg until smooth and well combined.

Using excess parchment as handles, remove cooled blondie from pan, and cut into squares. Drizzle with glaze; let stand until glaze is set, 15 to 20 minutes. Store in an airtight container for up to 3 days.