Chocolate Swiss Roll Cake

Name: Chocolate Swiss Roll Cake
Ingredients: 3/4 cup ( 100 g ) cake flour; 1/2 cup ( 56 g ) cocoa powder; 3 1/2 tablespoons ( 26 g ) cornstarch; 3/4 cups ( 170 g ) granulated sugar; 6 large eggs , room temperature; 1/2 teaspoon ( 3 g ) kosher salt; 4 tablespoons ( 58 g ) melted unsalted butter; 1 teaspoon vanilla extract; 2 tablespoons cocoa powder (for dusting the tea towel); 1 1/2 tablespoons cold water; 1 teaspoon plain gelatin powder; 1 1/2 cups heavy cream; 1/2 cup ( 50 g ) powdered sugar; 1 cup ( 170 g ) semi-sweet chocolate chips; 1/2 cup heavy cream; 1 teaspoon vanilla extract , optional