Preheat oven to 400°F (200°C). Line a 12-cup muffin tin with paper liners or grease well.

Prepare the rhubarb: In a small bowl, toss the chopped rhubarb with 1/4 cup of sugar and 1 tablespoon of flour until evenly coated. Set aside.

Combine dry ingredients: In a large bowl, whisk together the 2 cups of flour, 3/4 cup sugar, baking powder, baking soda, cinnamon, and salt.

Combine wet ingredients: In a separate medium bowl, whisk together the egg, milk, melted butter, and vanilla extract until combined.

Mix batter: Pour the wet ingredients into the dry ingredients. Mix gently with a spatula until just combined. Do not overmix; a few streaks of flour are acceptable.

Fold in rhubarb: Gently fold in about 3/4 of the prepared rhubarb mixture into the batter.

Fill and top: Divide the batter evenly among the 12 muffin cups, filling them about 2/3 full. Sprinkle the remaining rhubarb mixture over the top of each muffin.

Bake: Bake for 20 to 25 minutes, or until a toothpick inserted into the center of a muffin comes out clean. If the tops brown too quickly, lightly tent with foil for the last 5 minutes.

Cool: Let the muffins cool in the tin for 5 minutes before transferring them to a wire rack to cool completely.