Step 1

Preheat the oven to 350ºF (180ºC). Lightly butter a square 8 or 9-inch (20 or 23-cm) baking dish and line it with parchment paper.

Step 2

Whisk the buckwheat flour, cocoa powder, and salt together in a bowl. Set aside.

Step 3

Place a medium-sized pot on the stove with 1 to 2 inches of water inside. Find a heatproof medium-large bowl that sits snugly on top of the pot without touching the water. Bring the water to a boil. Add the dark chocolate and butter to the bowl and heat both together until smooth and melted, stirring occasionally.

Step 4

Remove the bowl from the pot and heat. Add both sugars to the melted chocolate and whisk to combine.

Step 5

Add the eggs to the chocolate, one at a time, whisking each until well blended. Add the vanilla and whisk well.

Step 6

Use a fine mesh sieve to sift the buckwheat flour into the chocolate mixture. Use a rubber spatula or wooden spoon to gently fold the brownie batter together until the flour is just mixed in. A few streaks of flour in the chocolate is ok.

Step 7

Pour the brownie batter into the prepared square pan. Bake the brownies for 28 to 30 minutes or until just set in the middle. Remove the brownies from the oven and transfer them to a wire rack. Let the brownies cool in the pan before slicing and serving.