Combine the Dry Ingredients: In a medium bowl, whisk together the white spelt flour, finely ground oat flour, fine sea salt, and sifted powdered sugar until evenly combined.
Cut in the Butter: Add the cold, diced butter to the flour mixture. Use a pastry blender or your fingertips to work the butter into the flour until the mixture resembles very coarse crumbs. Leave a few larger pieces of butter intact to help create a flaky crust.
Form the Dough: Add 5 tablespoons of ice-cold water and mix with your hands until the mixture comes together into a workable ball. Add the remaining water only if needed. If the dough becomes too wet, incorporate a little more flour.
Divide and Chill: Separate the dough into two portions, using roughly two-thirds for the base and one-third for the lattice. Flatten each portion into a disk, wrap them separately in plastic wrap, and refrigerate for 2 hours or overnight. Prepare the Tart Pan: Meanwhile, generously butter a 24 cm tart pan with a removable bottom.
Roll the Tart Base: Take the larger dough disk from the refrigerator and let it sit for 5–10 minutes to make rolling easier. On a lightly floured surface, roll the dough to about 3 mm thick and large enough to cover the bottom and sides of the tart pan. Line the Pan: Carefully drape the rolled dough over the tart pan and press it gently into place. Trim away excess dough if necessary, then crimp or tuck the edges neatly to fit the pan.
Prick the Pastry: Use a fork to prick the dough all over the bottom of the tart shell.
Add the Jam: Spread the 230 g jar of red currant jam evenly across the pastry base.
Create the Lattice: Remove the remaining dough from the refrigerator and roll it out on a lightly floured surface. Cut the dough into strips, then arrange them over the jam in a criss-cross lattice pattern.
Chill the Assembled Tart: Place the assembled tart in the refrigerator for 10–15 minutes while the oven preheats. This additional chilling helps reduce pastry shrinkage during baking. The prepared tart can also be refrigerated overnight and baked the following day. Preheat the Oven: Preheat the oven to 375°F / 180°C, or 160°C for an air-forced oven.
Brush the Pastry: When ready to bake, lightly brush the lattice and exposed pastry with beaten egg or milk. This helps create a crisp, shiny crust.
Bake the Torte: Bake for 35 minutes, or until the pastry is golden brown and the red currant filling is visibly bubbling.
Cool and Serve: Serve the Linzer Torte warm or cold, finished with a dusting of powdered sugar.
