01 -
Heat the oven to 375°F (190°C), and pop some cupcake liners into a muffin tin.
02 -
Stir together the sugar and diced rhubarb in a bowl, then leave it aside.
03 -
Whisk melted butter, milk, eggs, vanilla, and brown sugar in another bowl until smooth.
04 -
Toss in the flour, baking soda, baking powder, salt, and lemon zest. Mix only until there's no dry flour.
05 -
Carefully mix the rhubarb mixture into the batter, being sure not to overdo it.
06 -
Spoon the batter evenly into the prepared muffin cups.
07 -
Slide them into the oven and bake for 20-25 minutes. They're done when a toothpick comes out clean.
08 -
Let the muffins rest in the tin for about 5 minutes, then move them over to a wire rack to cool completely.