Preheat the oven to 350°F (175°C). Grease an 8x8-inch baking dish.
In a medium bowl, combine 1 ½ cups flour, ½ cup sugar, and ½ teaspoon salt. Add the softened butter and mix until crumbly. Press the mixture into the bottom of the prepared baking dish to form a crust.
In another bowl, whisk together the eggs, 1 cup sugar, ¼ cup flour, vanilla extract, and baking powder until smooth. Fold in the chopped rhubarb.
Pour the rhubarb mixture over the crust in the baking dish.
Bake for 35-40 minutes, or until the filling is set and the top is lightly golden.
Allow to cool completely in the pan before cutting into squares.