Preheat oven to 350 degrees Fahrenheit and prepare a 9x13 pan with parchment paper or grease lightly.

In a large bowl, mix butter, flour, sugar, baking powder, salt, and egg until crumbly.

Press half of the mixture evenly into the bottom of the pan to form the crust.

In another bowl, mix rhubarb, sugar, flour, and egg until well combined.

Spread the rhubarb mixture evenly over the crust layer.

Sprinkle remaining crumb mixture evenly over the top without pressing down.

Bake for 40 to 45 minutes until golden brown and set.

Cool completely before cutting into bars and serving.