2 teaspoons active dry yeast
1/4 cup (2 ounces) very warm water (105 to 115 degrees F)
Scant 1/3 cup plus 1/4 teaspoon (2 ounces) granulated sugar
3 cups plus 2 tablespoons (14 ounces) unbleached all-purpose flour
1/4 cup unsweetened cocoa powder
1 1/2 teaspoons Kosher salt
1 cup (8 ounces) warm brewed coffee (90 degrees F)
1 large egg yolk
2 teaspoons unsalted butter, softened
2/3 cup (4 ounces) chocolate chips
1/2 cup (4 ounces) cold water
1 1/4 teaspoons cornstarch