Chocolate Marble Cookies

2 cups (250 g), plus 1 tablespoon all-purpose flour, spooned and leveled (divided)

3/4 cup (95 g) bread flour, spooned and leveled

1 teaspoon baking soda

1 teaspoon cornstarch

3/4 teaspoon salt

1 cup (226 g) unsalted butter, cold and cubed

3/4 cup (150 g) light brown sugar

1/2 cup (100 g) granulated sugar

1 large egg, plus one egg yolk, room temperature

2 teaspoons vanilla extract

1 tablespoon Dutch process cocoa powder, sifted

4 ounces semi-sweet or bittersweet chocolate chips (or chopped chocolate bar), melted

1/2 cup semi-sweet chocolate chips, optional

Instructions: