Cupcake, because muffin batter and cupcake batter are made slightly differently
It’s still a cupcake because it’s cake and not muffin. Cake is a sweeter and fluffier kind of bread because it has more sugar and fat, whereas muffins are basically just dense bread.
It’s a half-eaten cupcake. You can take two wheels off a car, but that doesn’t make it a motorcycle.
When I see this question I can only be sad for people who can consider it perplexing. Yeah - if you have a sufficiently boring muffin and a sufficiently dense cake, you could see them as pretty similar but … eat better food.
Put some good stuff in your muffins (blueberries, poppy seeds, nuts, chocolate, etc) and learn to keep your cakes lighter and fluffier (especially for cupcakes) instead of rich like a muffin.
As others have said, they are different batters, the cooked result of both should be pretty noticeably different with it without frosting.
Unfrosted cake is still cake.
Muffins I believe are denser with more fat and less sugar. Though I see what you’re saying and we’re all just making excuses to eat dessert for breakfast sometimes.
