Preheat your oven to 350°F (175°C) and grease an 8×8-inch baking dish.

In a mixing bowl, combine softened butter and sugar. Cream together until light and fluffy.

Gradually add flour and salt to the creamed mixture. Mix until crumbly, then press into the baking dish. Bake for 10-12 minutes.

Remove the crust from the oven and let it cool for about 5 minutes.

In a separate bowl, whisk together sugar, flour, baking powder, salt, eggs, lemon zest, and lemon juice until smooth.

Gently fold in the rhubarb until combined.

Pour the filling over the baked crust evenly.

Bake for 35-40 minutes, until edges are golden and filling is set.

Cool completely on a wire rack, then dust with icing sugar before slicing.