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1
Preheat the oven to 350 degrees F. Brush an 11-by-17-inch jelly roll pan or rimmed baking sheet with vegetable oil and line with parchment paper; brush the paper with oil and dust with flour, tapping out the excess.
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2
Make the cake: Whisk the flour, baking powder, baking soda and salt in a medium bowl.
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3
Whisk the granulated sugar, vegetable oil, milk, eggs and vanilla in a large bowl.
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4
Add the flour mixture in 2 batches, whisking until incorporated.
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5
Transfer half of the batter (about 1 1/2 cups) to a separate bowl.
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6
Tint one batch red and the other batch blue with the food coloring.
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7
Spread the red and blue batters across the width of the prepared pan in alternating stripes, making each stripe about 2 inches wide (don't worry if the stripes aren't perfectly straight).
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8
Bake until the top springs back when pressed, 12 to 15 minutes.
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9
Let cool about 3 minutes in the pan.
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10
Dust with confectioners' sugar and spread a clean kitchen towel (not terry cloth) on top.
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11
Place a cooling rack on the towel, then invert the cake onto the rack; peel off the parchment.
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12
Roll up the cake and towel together, starting at a short end.
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13
Let cool completely on the rack, about 1 1/2 hours.
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14
Make the frosting: Beat the butter and salt in a large bowl with a mixer on medium speed until creamy, about 1 minute.
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15
Add the marshmallow cream and vanilla; beat on medium-high speed until fluffy, 2 to 3 more minutes.
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16
Beat in the confectioners' sugar, then beat in the milk (the frosting should be spreadable).
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17
Gently unroll the cake (don't worry if the ends are still curled up).
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18
Spread with half of the frosting all the way to the edges.
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19
Reroll the cake (without the towel) and trim the ends.
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20
Cover with the remaining frosting.
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21
Photograph by Kate Mathis
