vanilla crème filled chocolate cupcakes with bittersweet chocolate ganache

Name: vanilla-crème filled chocolate cupcakes with bittersweet chocolate ganache
Ingredients: chocolate cupcakes; 192 grams (1 cup) Golden Brown Sugar, packed; 48 grams (1/4 cup) Granulated White Sugar; 1 teaspoon Kosher Salt; 73 grams (1/2 cup plus 5 teaspoons) Millet Flour; 73 grams (1/2 cup plus 5 teaspoons) Garbanzo Fava Flour; 96 grams (1/2 cup) Potato Starch; 38 grams (1/4 cup plus 2 teaspoons) Arrowroot Starch; 3/4 teaspoon Xanthan Gum; 2 teaspoons Baking Soda; 2 teaspoons Instant Espresso Powder; 60 grams (3/4 cup) Unsweetened Dutch-process Cocoa Powder; 4 ounces (1/2 cup or 113 grams) Canola Oil; 16 ounces (2 cups or 454 grams) Buttermilk; 2 large Eggs, bring to room temperature; 2 teaspoons (10 grams) Vanilla Extract; Unsalted Butter; vanilla-crème filled chocolate cupcakes with bittersweet chocolate ganache; 1 recipe Chocolate Cupcakes (above); 114 grams (8 tablespoons) Unsalted Butter, softened; 7.5 ounces jar (213 grams) Marshmallow Fluff; 1 1/2 teaspoons (7 grams) Vanilla Extract; 1 1/2 cups (180 grams) Powdered Sugar, sift after measuring; 6 ounces (3/4 cup or 170 grams) Heavy Cream; 6 ounces Bittersweet Chocolate (not unsweetened)²; 2 ounces White Chocolate