Step 1

Position a rack in the middle of the oven and preheat to 350 degrees. Line an 8-inch square baking pan with parchment paper.

Step 2

Coarsely chop the chocolate. Transfer a generous 2 3/4 ounces (80 grams) of it to a large microwave-safe bowl and set aside the remaining chocolate.

Step 3

In a microwave, melt the chocolate on high in 20-second bursts, stirring after each burst, until fully melted. (Alternatively, set a heatproof bowl over a pan with 1/2 inch of gently simmering water — make sure the bottom of the bowl doesn’t touch the water — and melt the chocolate, stirring occasionally with a silicone spatula. Remove the bowl from the heat.)

Step 4

Whisk in the milk, granulated and brown sugars, oil and vanilla until well combined; the batter should look lush and glossy.

Step 5

Sift in the flour, cocoa powder, baking powder and salt, and whisk just until combined. Fold in the remaining chocolate just to combine; the batter will be thick.

Step 6

Transfer the batter to the prepared pan and use an offset spatula to smooth it out.

Step 7

Bake for 25 to 30 minutes, or until the brownie is set on top and has puffed around the edges and in the middle and a cake tester inserted in the middle of the pan comes out with a few moist crumbs. Transfer to a wire rack and let cool for at least 30 minutes. The center of the brownie block might deflate a bit; this is fine.

Step 8

When ready to serve, cut into nine (2 1/2-inch) squares and serve.