1-Preheat the oven: Preheat the oven to 350°F (175°C) and grease and line an 18 x 13-inch baking pan with parchment paper.

2-Whisk dry ingredients: In a separate bowl, whisk together the cake flour, baking powder, and salt.

3-Cream butter, oil, and sugar: In a mixing bowl, cream together the unsalted butter, vegetable oil, and granulated sugar until light and fluffy.

4-Add eggs: Add the eggs and egg whites one at a time, beating well after each addition.

5-Stir in sour cream and vanilla: Stir in the sour cream and vanilla extract.

6-Fold in dry and wet ingredients: Alternately fold in the dry flour mixture and buttermilk in three additions, starting and ending with the flour mixture, mixing gently to avoid overmixing.

7-Bake the batter: Pour the batter into the prepared pan and bake for 35 to 40 minutes, or until a toothpick inserted in the center comes out clean.

8-Cool the cake: Allow the cake to cool completely before proceeding.

9-Prepare marshmallow filling: Once the cake is cool, it’s time for the marshmallow filling. Beat the softened butter until smooth, then add marshmallow fluff, powdered sugar, vanilla extract, milk or cream, and salt. Beat on medium speed until light and fluffy, and tint a portion red for piping.

10-Assemble and decorate: For assembly to decoration, chill the cake for easier cutting, cut out tree shapes, slice each horizontally, pipe filling onto one layer, and sandwich with the other. Melt white chocolate with coconut oil, dip the trees, let excess drip off, place on parchment to set, pipe red frosting in a zigzag, and sprinkle with green sprinkles. Chill until firm. This step-by-step approach keeps things easy and enjoyable.