Preheat oven to 325°F (170°C). Spray a 9x5-inch loaf pan with baking spray with flour. Line pan with parchment paper, letting excess extend over sides of pan.
In a large bowl, whisk together melted butter, granulated sugar, and 3 tablespoons (39 grams) brandy. Whisk in 2 cups (275 grams) melted ice cream and eggs. Whisk in flour, baking powder, and salt until smooth.
Place 1 cup (325 grams) batter in a small bowl, and whisk in cocoa and remaining ½ cup (75 grams) melted ice cream. Whisk nutmeg into remaining batter; batters will be thick. Pour half of nutmeg batter into prepared pan. Pour cocoa batter on top. Pour remaining nutmeg batter on top. Using a knife, swirl batters together.
Bake until a wooden pick inserted in center comes out clean, 50 minutes to 1 hour. Let cool in pan for 10 minutes. Using a wooden pick, poke warm cake all over, and drizzle with remaining 1 tablespoon (13 grams) brandy. Let cool slightly. Using excess parchment as handles, remove from pan. Let cool completely on a wire rack. Just before serving, dust with confectioners’ sugar.
Recipe by Bake from Scratch at https://www.bakefromscratch.com/brandy-alexander-marble-cake/