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. Stir until well mixed.

In another bowl, whisk together the buttermilk, egg, vanilla extract, and melted butter until smooth.

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

Using a spoon or ice cream scoop, drop spoonfuls of the batter onto the prepared baking sheet, leaving space between each fritter.

Bake for 15-20 minutes, or until the fritters are golden brown and a toothpick inserted into 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.