Step 1

Adjust the oven rack to a lower-middle position and preheat the oven to 375°F (191°C).

Step 2

Butter a 2-quart (1.9 l) souffle dish, then coat the dish evenly with 1 tablespoon sugar and refrigerate until ready to use.

Step 3

In a medium or large heatproof bowl set over a saucepan filled with 1 inch (25 mm) barely simmering water, melt the chocolate with 4 tablespoons butter, making sure the water doesn’t touch the bottom of the bowl and stirring the mixture occasionally until smooth.

Step 4

Stir in the liqueur, vanilla, and salt. Remove from the heat and let cool slightly.

Step 5

Using a stand mixer fitted with the paddle attachment on medium speed, beat the egg yolks and 1/3 cup sugar until thick and pale yellow, 3 to 5 minutes.

Step 6

Fold the beaten egg yolk mixture into the chocolate mixture.

Step 7

Using a clean, dry mixer bowl and whisk attachment on medium-low speed, beat the egg whites and cream of tartar until foamy, about 1 minute. Increase the speed to medium-high and beat until stiff peaks form, 3 to 4 minutes.

Step 8

Using a silicone spatula, vigorously stir 1/4 of the beaten egg whites into the chocolate mixture. Then gently fold in the remaining whites just until incorporated.

Step 9

Transfer the mixture to the prepared dish and bake until fragrant, fully risen, and the exterior is set but the interior is still a bit loose and creamy but not soupy, 25 to 30 minutes.☞TESTER TIP: To check doneness, use 2 large spoons to gently pull open the top and quickly peek inside the souffle.

Step 10

Serve the souffle immediately by bringing the dish to the table, accepting oohs and aahs, and then spooning it into individual dishes.