Preheat oven to 325°F. Line a 9-inch spring form pan with parchment paper, and spray with baking spray with flour.

In the top of a double boiler, place chocolate and butter.

Cook over simmering water, stirring occasionally, until mixture is smooth. Remove from heat, and let cool for 10 minutes.

In the bowl of a stand mixer fitted with the paddle attachment, beat eggs, sugar, cardamom, and salt at medium-high speed until light and thickened, 6 to 8 minutes. Fold in melted chocolate until combined. Pour batter into prepared pan

Bake until a wooden pick inserted in center comes out clean, about 1 hour and 10 minutes. Let cool completely on a wire rack. To serve, gently remove ring from spring form pan. Dust cake with cocoa.