Mix all dry ingredients, place them on a work surface or large bowl, then make a well in the center.

Add the vegan butter cubes, lemon zest, and eggs. Mix with your fingers until the dough looks like coarse crumbs.

Slightly knead the dough until it holds together, wrap it with cling film, shape it into a ball, and refrigerate for at least an hour.

Use a stand mixer with a paddle attachment to avoid getting your hands messy.

Warm the oat milk in a saucepan. In a bowl, combine 1/3 of warm (not hot) oat milk, egg yolks, sugar, vanilla, and cornstarch. Stir the mixture thoroughly until the cornstarch is fully dissolved.

Mix the custard mixture into the remaining warm milk. Cook over low-medium heat while constantly whisking until it thickens.

Take the custard cream off the heat. Strain it to remove lumps.

Add the zest and cold vegan butter. Set aside in the fridge to chill.

Roll the cold dough between two sheets of baking paper to a thickness of 3-4 cm (1/4 inch). Use dough measuring strips for an even thickness.

Lift the dough to a pie dish or tart ring using a rolling pin. Press the dough well on the sides, then prick the bottom with a fork. Trim the edges. Let the dough rest in the fridge for 20 minutes.

Pour the cold lemon custard on the prepared pie dough.

Bake in a preheated oven for 320° F (160° C) for 55 minutes. Adjust the temperature to 355° F (180° C), then bake for another 8 to 10 minutes.

Let the pie cool completely before sprinkling powdered sugar. It’s ready to cut and serve.