For the cupcakes:
½ cup plus 2 tbsp. cake flour
1/3 cup Dutch-process cocoa powder
½ tsp. baking powder
¼ tsp. baking soda
1/8 tsp. salt
2 large eggs, separated and at room temperature
1/3 cup canola oil
½ cup plus 2 tbsp. sugar
2 tbsp. water
For the filling:
6 tbsp. unsalted butter, softened
1 ½ cups confectioners’ sugar
¾ cup Marshmallow Fluff
1 ½ tbsp. plus 1 tsp. heavy cream
For the frosting:
¼ cup heavy cream
4 oz. bittersweet chocolate, finely chopped
1 tbsp. unsalted butter, softened
Preheat the oven to 350°. Lightly coat the wells of a muffin tin with non-stick cooking spray, or line with paper liners.
In a medium bowl, whisk together flour, cocoa powder, baking powder, baking soda, and salt. Set aside.
In a large mixing bowl, beat together egg yolks, canola oil, ½ cup sugar and water until well combined. Add the dry ingredients and stir until just combined.
In a clean medium bowl, beat egg whites at high speed until soft peaks form. Gradually add remaining 2 tablespoons sugar and beat until stiff and glossy. Beat one quarter of the egg whites into the batter to lighten the mixture. Add remaining whites and gently fold the mixture together until no streaks remain.
Evenly divide the batter between the wells of the prepared muffin tin. Bake until the cupcakes spring back when lightly touched in the center, about 13-16 minutes. Remove from oven and allow to cool slightly in pan before transferring them to a wire rack to cool completely.
To make the filling, in a medium bowl beat together the butter, confectioners’ sugar, Marshmallow Fluff and 1 ½ tablespoons of the heavy cream until fluffy. Reserve ½ cup of the mixture – transfer the rest to a pastry bag fitted with a ¼ – inch round tip. Beat the remaining 1 teaspoon of cream into the reserved ½ cup of filling, cover and reserve.
Gently insert the tip of the pastry bag about ½ – inch deep into the top of each cupcake and lightly squeeze in some of the filling.
To make the frosting, in a small saucepan heat cream over medium heat until steaming, stirring constantly. Remove from the heat, add the chocolate and let stand for 5 minutes. Add the butter and stir until smooth. Transfer to a small bowl and dip the top of each cupcake to thoroughly coat. Spoon the reserved filling into a pastry bag fitted with a very small plain tip and pipe curlicues across the center of each cupcake. Refrigerate the cupcakes for 10 minutes to set the frosting.