Marshmallow Stuffed Hot Chocolate Cake

Name: Marshmallow-Stuffed Hot Chocolate Cake
Ingredients: ½ cup (120 g) sour cream, at room temperature; ½ cup (120 g) whole milk, at room temperature; ½ cup (112 g) canola oil; 3 large eggs, at room temperature; 1 tsp. pure vanilla extract; 2 cups (284 g) all-purpose flour; 1 cup (200 g) granulated sugar; 1 cup (200 g) light brown sugar; ¾ cup (75 g) Dutch-process cocoa powder; 2 tsp. baking soda; 1 tsp. baking powder; 1 tsp. salt; 1 cup (240 g) strong, freshly brewed coffee, hot; 8 Tbsp. (1 stick or 113 g) unsalted butter, at room temperature; Pinch salt; 1 cup (120 g) confectioners’ sugar; 2 cups (280 g) Marshmallow Fluff; 2 Tbsp. heavy cream; 8 oz (226 g) semisweet or bittersweet chocolate; ½ cup (120 g) heavy cream; Marshmallows, cut into cubes and toasted