Preheat oven to 400°.

Coat two 6-oz. soufflé cups with butter and sprinkle with sugar. Chill cups on a baking sheet while preparing batter.

Melt chocolate chips with milk, liqueur, espresso powder, cornstarch, ½ tsp. sugar, and cinnamon in a saucepan over medium heat, whisking until smooth.

Combine yolk and vanilla, then whisk into chocolate mixture. Cook 2 minutes, remove from heat, and cool to room temperature.

Beat egg white with cream of tartar and salt, using an electric mixer on high speed, until soft peaks form. Gradually add remaining 1½ tsp. sugar; continue beating until stiff peaks form (whites stand up when beaters are lifted from bowl). Using a whisk, blend whites into chocolate mixture until there are no streaks. Fill prepared cups with batter. Bake on the baking sheet until soufflés puff, about 20 minutes. Test for doneness by inserting a skewer into the center of a soufflé — soufflé is done when skewer comes out clean or slightly moist.

To serve, cut a small slit in top of each soufflé. Pour Dulce de Leche Sauce into soufflés, allowing sauce to pool and drip down sides.

Garnish soufflés with whipped cream and pecans. Serve immediately.