Preheat your oven to 400°F (200°C). Lightly grease a baking sheet or line it with parchment paper.

In a medium bowl, combine the chopped rhubarb, 1/4 cup sugar, and vanilla extract. Toss gently to coat and set aside for 10 minutes to allow the rhubarb to macerate slightly.

In a separate large bowl, whisk together the flour, baking powder, 1/4 cup sugar, and salt.

In a small bowl, whisk together the egg, milk, and melted butter. Pour the wet ingredients into the dry ingredients and stir just until combined. Do not overmix; a few lumps are acceptable.

Gently fold the macerated rhubarb mixture into the batter, distributing it evenly.

Drop heaping tablespoons of batter evenly onto the prepared baking sheet, spacing them about 2 inches apart. They should resemble thick drop biscuits.

Bake for 15 to 18 minutes, or until the edges are golden brown and the centers are set.

Remove from the oven and immediately sprinkle the tops of the warm fritters generously with extra granulated sugar before transferring them to a wire rack to cool slightly.