Begin by creaming the butter and powdered sugar together until the mixture becomes pale, smooth, and airy. It should feel light and fluffy when stirred, with no visible sugar grains remaining.

Add the whisked egg and a splash of vanilla to the butter mixture. Mix thoroughly until well incorporated, forming a smooth base.

Sift the flour in two portions and gently fold each batch into the egg mixture. Add the salt and continue mixing until a soft dough starts to come together. Use your hands to knead it lightly into a uniform, pliable dough, being careful not to overwork it. Wrap and chill if desired before shaping into tart molds.