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Preheat the oven to 350 degrees F. Line a 12-count cupcake pan with paper liners (or grease the pan).
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In a liquid measuring cup, measure out the oat milk and add the vinegar. Let sit for a few minutes.
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In a mixing bowl, combine the flour, baking powder, baking soda, and salt. Stir well.
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Add the sugar, oil, egg, vanilla extract, and the oat milk/vinegar mixture. Stir until well combined.
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Divide the batter between two bowls. Use the food coloring to create one bowl of yellow batter and one bowl of orange batter.
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Pour the yellow batter into the lined cupcake pan wells, filling each around ⅓- to ½-way full. Gently pour the orange batter on top, dividing evenly among the cupcake pan wells, so that each one is at least ¾ full.
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Bake the cupcakes at 350 degrees F on the center rack for 15-19 minutes, or until cooked through and a toothpick pulls clean from the center. Let cool in the pan for 10 minutes, then remove to a cooling rack.
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Meanwhile, prepare the frosting: combine the softened dairy-free butter, powdered sugar, vanilla, and 1 tablespoon of oat milk. Beat using the whisk attachment on a stand mixer or hand mixer, starting on low then increasing speed to high, until light and fluffy. Add additional non-dairy milk if needed to reach the preferred consistency.
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Pipe or spread the frosting on the cooled cupcakes. Top with sprinkles and a couple pieces of candy corn. Enjoy!