Position a rack in the lower third of your Oven and preheat to 375°F. Place a Baking Sheet on the rack to preheat as well — baking the soufflés on a hot surface gives them a strong bottom-up lift.

Using a Pastry Brush, generously coat the inside of four 6 oz Ramekins with softened 1 tbsp unsalted butter, 软化 (软化，用于涂抹陶土杯), brushing in vertical strokes from the bottom up (this helps the soufflé climb straight). Chill for 5 minutes, then coat each with 2 tbsp sugar, 细砂 (用于涂抹陶土杯), rotating to cover all surfaces. Tap out any excess. Set aside in the fridge.

Combine the chopped 4 oz dark chocolate, 细切 (70%可可，细切) and 2 tablespoons of 1 tbsp unsalted butter, 软化 (软化，用于涂抹陶土杯) in a heatproof Mixing Bowl set over a small Saucepan of barely simmering water (do not let the bowl touch the water). Stir gently until fully melted and smooth. Remove from heat and let cool slightly, about 3–4 minutes.

In the same Saucepan (wiped clean), whisk together the 3 tbsp milk, 1 tbsp all-purpose flour, and 1 tablespoon of the 2 tbsp sugar, 细砂 (用于涂抹陶土杯) over medium-low heat. Cook, whisking constantly, for 1–2 minutes until the mixture thickens into a smooth paste (a very loose roux). Remove from heat.

Whisk the 3 tbsp milk-1 tbsp all-purpose flour paste into the melted 4 oz dark chocolate, 细切 (70%可可，细切) until fully combined and smooth. Whisk in the 3 3 eggs (分开，室温) one at a time, then add the 1 tsp vanilla extract and 1 pinch of fine salt. The base should be thick, glossy, and completely smooth. Set aside.

In the bowl of a Stand Mixer (or a large, very clean Mixing Bowl using a Hand Mixer), add the 3 3 eggs (分开，室温) and 1 pinch of cream of tartar. Beat on medium speed until foamy, about 1 minute. Increase to medium-high and gradually add the remaining 2 tablespoons of 2 tbsp sugar, 细砂 (用于涂抹陶土杯). Continue beating until stiff, glossy peaks form — the meringue should hold a firm peak but not look dry or clumpy, about 3–4 minutes total.

Using a Spatula, fold about one-quarter of the meringue into the 4 oz dark chocolate, 细切 (70%可可，细切) base to lighten it — stir this first addition in without worrying about deflating. Then gently fold in the remaining meringue in two additions, using wide, sweeping strokes from the bottom of the bowl up and over. Stop folding as soon as no white streaks remain; do not overmix.

Remove the prepared Ramekins from the fridge. Divide the soufflé batter evenly among them, filling each to about ½ inch below the rim. Run your thumb around the inside rim of each Ramekins to create a shallow groove (this helps the soufflé rise straight and form a classic 'top hat').

Place the filled Ramekins on the preheated Baking Sheet in the Oven. Bake for 11–13 minutes. At 11 minutes, the soufflés will have a very jiggly, molten center. At 13 minutes, they'll be just set with a slightly creamy interior. Do NOT open the oven door during the first 10 minutes of baking.

Remove from the Oven and serve immediately — soufflés wait for no one! If desired, dust lightly with 1 tbsp unsweetened cocoa powder (optional) (用于撒粉) using a fine mesh Sieve, and serve with a scoop of 1 cup vanilla ice cream (optional) (用于上菜) or a dollop of whipped cream on the side to spoon into the center at the table.