Preheat your oven to 350°F (175°C) and grease a 9×13-inch baking pan.

Cream 1 cup of softened unsalted butter and 1½ cups of granulated sugar together until light and fluffy.

Add 4 large eggs one at a time, mixing well after each addition, then stir in 2 teaspoons of vanilla extract.

In a separate bowl, whisk together 2½ cups of flour, 2 teaspoons of baking powder, and ½ teaspoon of salt.

Gradually add the dry mixture into the butter and egg mixture, stirring until just combined.

Toss 3 to 4 cups of chopped rhubarb in 2 tablespoons of flour, then fold into the batter.

Spread the batter into the prepared baking pan evenly.

Bake for 45 to 50 minutes until golden brown and a toothpick inserted comes out clean.

Cool in the pan for 30 minutes, then dust with powdered sugar before serving.