Preheat your oven to 350°F (175°C). Prepare a 9x9 inch baking dish by greasing it well to prevent sticking.

In a medium bowl, combine the chopped rhubarb and half of the sugar. Let this mixture sit for about 15 minutes to release its juices.

In another mixing bowl, cream together the softened butter and the remaining sugar until smooth and fluffy.

Stir in the vanilla extract, then add the eggs one at a time, ensuring each egg is well incorporated.

In a separate bowl, whisk together the flour, baking powder, and salt. Gradually add this dry mixture to the wet ingredients, mixing on low until just blended.

Fold the rhubarb mixture gently into the batter, ensuring it is evenly distributed.

Pour the batter into the prepared baking dish and spread evenly.

Bake in the preheated oven for 30-35 minutes, or until a toothpick inserted comes out clean.

Remove from the oven and allow to cool in the pan before cutting into bars.