Preheat the oven to 400°F (conventional, bottom rod).

Prepare a 14-ounce ramekin by generously brushing it with butter and dusting with granulated sugar. Shake off the excess.

In a heatproof bowl, mix the chocolate, butter, salt, and coffee powder. Heat over a double boiler, stirring until the chocolate and butter melt, creating a smooth, shiny mixture. Remove from heat and set aside.

Separate the eggs, ensuring no yolk gets into the egg white.

Place egg whites in a clean bowl and beat at medium speed with an electric beater until frothy (about 1-2 minutes). Gradually add sugar while continuing to whisk until you achieve a shiny, glossy, and stiff meringue with stiff peaks.

Add the yolks to the chocolate mixture and whisk to combine.

Gently fold a third of the meringue into the chocolate mixture, then add the remaining meringue. Be cautious not to overmix.

Transfer the batter to the prepared ramekin, spreading it out. Use a knife to create a gap along the edge to prevent the batter from touching the edges of the ramekin.

Place it in the oven and immediately reduce the heat to 375°F.

Bake for 18-20 minutes until the soufflé forms a thin crust on top and lightly wobbles in the center.

Serve warm, dusted with powdered sugar and your favorite toppings!