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1
Preheat oven to 350F.
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2
Line a buttered 8-inch square baking pan with parchment, allowing a 2-inch overhang.
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3
Butter lining (not overhang).
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4
Stir together 1 tablespoon of sugar, the condensed milk, coconut, egg white, and 1/4 teaspoon of the vanilla in a bowl.
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5
Put butter and both chocolates in a heatproof bowl set over a pan of simmering water; stir until melted.
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6
Let cool slightly.
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7
Whisk together flour, baking powder, and salt in a bowl.
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8
Whisk remaining 3/4 cup sugar into chocolate mixture.
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9
Add eggs; whisk until mixture is smooth.
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10
Stir in remaining 2 teaspoons vanilla.
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11
Add flour mixture; stir until well combined.
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12
Pour one-third of chocolate batter into prepared pan.
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13
Spread evenly with an offset spatula.
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14
Drop dollops of coconut mixture (about 1 tablespoon each) on top of batter, spacing about 1 inch apart.
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15
Drizzle remaining batter on top, and gently spread to fill pan.
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16
Drop dollops of remaining coconut mixture on top.
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17
Gently swirl coconut mixture into batter with a butter knife, running the knife lengthwise and crosswise through layers.
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18
Bake until a cake tester inserted into brownies (avoid center and edges) comes out with a few crumbs but is not wet, 35 to 40 minutes.
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19
Let cool slightly in pan, about 15 minutes.
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20
Lift out; let cool completely on a wire rack before cutting into squares.
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21
Brownies can be stored between layers of parchment in an airtight container at room temperature up to 2 days.
