Preheat the oven to 350ºF. Brush vegetable oil on the bottom and sides of a half sheet pan (18”x13”). Line with parchment paper, brushing vegetable oil on the parchment as well. Sprinkle flour over the pan and tap out the excess.

Whisk together the flour, baking powder, baking soda, and salt in a large bowl.

In another bowl, whisk the oil, sugar, milk, eggs, and vanilla together. Add the wet ingredients to the dry ingredients, mixing until just combined.

Pour half of the batter into another bowl and add red food coloring to one half and blue to the other. Mix until combined.

Spread the red and blue batter in alternating stripes in the pan, aiming for about 2 inches wide.

Bake in the preheated oven for about 15 minutes until the top springs back when pressed.

Let the cake cool for 3 minutes, then loosen the edges with a knife. Dust the top of the cake with powdered sugar, cover with a kitchen towel, and invert onto a cooling rack.

Remove the parchment paper and roll the cake up with the towel starting from the long end. Allow it to cool completely for at least 1 1/2 hours.

To make the frosting, beat the butter and salt in a stand mixer until light and creamy, about 1 minute.

Add marshmallow cream and vanilla, continuing to beat for 2-3 minutes. Gradually add powdered sugar, then milk one tablespoon at a time until reaching a spreadable consistency.

Gently unroll the cake, spread half of the frosting over it, then re-roll without the towel. Trim the edges and frost the outside with the remaining frosting.