Preheat the oven to 350 degrees F.
In a small bowl, mix the oat milk (1 cup minus 1 tbsp from it) with the 1 tbsp of lemon juice. Let it sit for 10 minutes.
After 10 minutes, beat the oat milk, vanilla, sugar, butter and vegan egg with a mixer in a large bowl until well mixed.
In another large bowl, mix together the flour, baking powder and salt.
Slowly stir the dry ingredients into the wet ingredients until a batter forms. Lastly, stir in the sprinkles.
Place the cupcake liners into 18 sections. Evenly add the batter into each liner.
Bake for 30 minutes, then remove from the oven and let cool on a heatproof surface for at least 10 minutes. They will cook more as they cool down.
Frost the cupcakes with your favorite vegan icing and top with sprinkles. Enjoy!