Make the shortbread base by crumbling the butter with the flour and white sugar.
Press the cookie base into a baking dish and bake until golden brown.
Cook the cranberries with the sugar until they pop.
The cranberries should be thick and jammy.
Whip the eggs with a hand mixer.
Beat in brown sugar, vanilla, baking powder, and salt.
Fold in the cooled cranberry mixture.
Pour the filling over the pre-baked base.