Preheat your oven to 375°F (190°C) and line a baking sheet with parchment paper.

In a medium bowl, combine the chopped rhubarb, flour, sugar, baking powder, baking soda, salt, and cinnamon. Mix well to ensure the rhubarb is evenly coated with the dry ingredients.

In a separate bowl, whisk together the buttermilk, egg, vanilla extract, and melted butter until well combined.

Pour the wet ingredients into the dry ingredients and stir gently until just combined. Be careful not to overmix; a few lumps are okay.

Using a spoon or a cookie scoop, drop heaping tablespoons of the batter onto the prepared baking sheet, leaving space between each fritter.

Bake in the preheated oven for 15-20 minutes, or until the fritters are golden brown and a toothpick inserted in the center comes out clean.

Allow the fritters to cool slightly on the baking sheet before transferring them to a wire rack. Dust with powdered sugar if desired before serving.