Preheat the oven to 350°F (175°C) and grease a 9-inch baking pan.
Combine the chopped rhubarb with 1/4 cup of sugar in a bowl, tossing to coat. Let sit for 10 minutes until slightly glazed and juices begin to form.
2 cups fresh rhubarb stalks
In a large mixing bowl, whisk together flour, baking powder, baking soda, salt, and remaining 3/4 cup sugar. Set aside.
2 cups fresh rhubarb stalks
Add the melted butter, eggs, and vanilla extract to the dry ingredients. Whisk until smooth and batter is slightly thickened, about 1-2 minutes.
2 cups fresh rhubarb stalks
Fold the drained rhubarb into the batter using a rubber spatula, distributing evenly. The batter will be thick but moist.
2 cups fresh rhubarb stalks
Pour the batter into the prepared baking pan, spreading evenly with a spatula. Bake for 50 minutes, or until the top is golden and a toothpick inserted in the center comes out clean.
Remove from oven and allow to cool slightly before slicing. The cake will have a moist crumb with vibrant pink streaks of rhubarb visible through the crust.