Preheat your oven to 350˚F and spray an 18-by-13-inch half-sheet pan with nonstick baking spray that contains flour.

In a medium bowl, whisk together the all-purpose flour, baking powder, baking soda, and kosher salt.

In a large bowl, whisk the granulated sugar and eggs until foamy and lightened in color, about 1 to 2 minutes. Then whisk in the vegetable oil and vanilla extract.

Gradually add the flour mixture to the wet ingredients, alternating with the buttermilk, starting and ending with the flour mixture. Whisk well after each addition.

Pour the batter into the prepared sheet pan and smooth the top. Bake for about 20 minutes or until the cake is lightly golden and a toothpick inserted in the center comes out clean. Allow the cake to cool completely in the pan, at least 1 hour, before frosting.

Using a stand mixer or hand mixer, beat the salted butter on medium-high speed until light and fluffy, about 2 to 3 minutes. Reduce speed to low, add half of the powdered sugar and mix until combined. Add the milk and vanilla extract, mixing to incorporate. Then add the remaining powdered sugar and mix until fully blended. Increase speed to medium-high and continue beating until fluffy, about 3 minutes.

Spread about 3 cups of the buttercream in a smooth, even layer over the cooled cake.

Transfer 1/4 cup of the remaining frosting into a piping bag with a small opening. Add forest green gel food coloring to the rest of the frosting until a deep green shade is achieved. Transfer this green frosting to a separate piping bag fitted with a larger opening.

Lightly trace a large triangle on the frosted cake to mark the Christmas tree’s body. Place 5 brown mini candy-coated chocolates per row in 3 rows centered directly below the triangle to create the tree trunk.

Using the green buttercream, pipe a row of 3/4-inch dots across the bottom of the triangle just above the trunk. Drag each frosting dot downward and outward to create curved branches. Pipe additional rows of dots above the first, overlapping each row until the entire triangle is covered.

Sprinkle the red, green, and white holiday sprinkles around the cake border. Pipe small dots across the surrounding white icing to simulate snow.

Pipe swooping lines of the white frosting across the tree to mimic garlands. Press the yellow mini candy-coated chocolates onto the white lines spaced about 1 inch apart. Press the red mini candy-coated chocolates flat on the green branches to resemble ornaments.

Cut the 6-inch red sour candy belt lengthwise in half, fold one strip into a bow shape, and place it atop the tree.