Step 1

Stir sugar and yeast into ⅔ cup warm (100°) water in a small bowl. Let sit until foamy, about 5 minutes. Whisk flour, corn muffin mix, salt, and baking powder in a large bowl to combine. Stir sugar mixture into dry ingredients, then stir in 2 Tbsp. oil. Mix just until a shaggy dough forms.

Step 2

Turn dough out onto a work surface. Gently knead just until smooth (be careful not to overwork). Transfer to a lightly oiled bowl and cover tightly with plastic wrap. Let rise in a warm spot until dough is puffed and yields easily when poked, about 1½ hours.

Step 3

Divide dough into 16 balls and gently roll between your palms until smooth. Roll out each ball to a 6x3" oval, lightly brush with oil, then fold in half crosswise. Cover bao with a damp cloth and let rise until slightly puffy, 60–90 minutes.

Step 4

Place a bamboo steamer lined with parchment paper over a large pot of simmering water (or you can use a steamer basket). Steam bao in batches until firm to the touch and cooked through, 10–12 minutes per batch.

Step 5

Do Ahead: Dough can be made 12 hours ahead; chill instead of letting rise. Let rise 2 hours. Bao can be steamed 1 week ahead; tightly wrap and freeze. Thaw and steam 3 minutes to restore softness just before serving.

Step 6

Cook sugar and soy sauce in a small saucepan over medium heat, stirring often, until sugar is dissolved; let cool.

Step 7

Transfer to a small bowl and mix in chile, ginger, garlic, dark soy sauce, mushroom soy sauce, vinegar, and pepper. Let black pepper sauce sit 30 minutes to allow flavors to meld.

Step 8

Build sandwiches with bao using turkey, black pepper sauce, mayonnaise, pickles, carrots, and cilantro.

Step 9

Do Ahead: Sauce can be made 3 days ahead. Cover and chill.