Preheat oven to 375°F (190°C). Line bottom of copper soufflé pan with parchment paper. Brush pan with 1 tablespoon (14 grams) butter. Spoon 1 tablespoon (12 grams) sugar into pan, and rotate so pan is fully coated with sugar; pour out excess.

In the top of a double boiler, place chocolate and remaining 7 tablespoons (98 grams) butter. Cook over simmering water, stirring occasionally, until melted and smooth. Remove from heat, and whisk in 2½ tablespoons (36 grams) sugar until well combined. Stir in egg yolks and flour.

In the bowl of a stand mixer fitted with the whisk attachment, beat egg whites and salt at medium-high speed until soft peaks form. Gradually add remaining 4 tablespoons (50 grams) sugar, 1 tablespoon (12 grams) at a time, beating until glossy stiff peaks form.

Using a balloon whisk, fold one-third of egg white mixture into chocolate mixture until just a few white streaks remain. Gently fold in remaining egg white mixture just until combined. (Be careful not to overmix.) Carefully pour into prepared pan.

Bake until soufflé has risen and top begins to crack, 25 to 30 minutes. Let cool completely in pan on a wire rack. Serve with Sweetened Whipped Cream.