The Kitchn: Delight your inner child with this oversized DIY Swiss roll
1 teaspoon vanilla extract
3/4 cup all-purpose flour
1/4 cup dark cocoa powder, such as Hershey's Special Dark
1 teaspoon baking powder
1/2 teaspoon kosher salt
For the filling:
8 tablespoons (1 stick) unsalted butter, at room temperature
1/2 cup vegetable shortening, at room temperature
1 (7-ounce) jar marshmallow fluff
3 cups powdered sugar
...continued