1Preheat the oven to 375F.
2In a medium bowl, combine the flour, sugar and salt. Grate in the butter or lard using the coarse side of a box grater, or cut it into bits. Blend it into the flour with a fork, pastry cutter or your fingers, until it’s crumbly, with bits of butter the size of a pea remaining. Add the water and stir just until the dough comes together.
3Shape it into a disk, and on a lightly floured surface, roll it out into about a 12-inch circle. Drape over a 10-inch tart pan with a removable bottom, and gently press it in to fit into the bottom and sides. Use the rolling pin to roll across the edge of the pan to cut the pastry cleanly away; discard any scraps.
4Place a piece of foil or parchment in the pastry and fill with pie weights; bake for 15 minutes, then remove the weights and foil and bake for another 10 minutes, or until golden. Remove and set aside to cool.
5Meanwhile, in a medium saucepan, bring the cranberries, sugar, and lemon zest and juice to a simmer. Cook for 10-15 minutes, until the berries pop and soften. Set a colander over a bowl and pour in the sauce; stir and press down on the solids to extract as much as possible. (You could save the solids for a smoothie.) Add the butter and set aside to cool.
6Once the butter has melted (there can still be a few solid bits in there), whisk in the eggs and return the mixture to the pan. Bring it to a simmer over medium-low heat, whisking constantly until it bubbles and thickens. If there are little bits of egg, lemon or cranberry you want to get rid of, pour it through a sieve into another bowl. Pour into the shell while it’s still warm, and let stand at room temperature until cooled and set.