1. Start with the dough by mixing the cold water with the apple cider vinegar. Place in the fridge (or add an ice cube) to cool it down even more. Add the flour, salt, and xylitol (or sugar) to a large bowl and mix to combine. Add the cold butter in small pieces and cut with a pastry blender* into even smaller, pea-sized pieces. Gradually add the cold vinegar water and work it in. Work quickly here so the dough and butter are not warming up. Knead until the dough starts coming together. The dough should not be wet or sticky, so don’t add too much liquid. Wrap the dough in plastic wrap and place it in the fridge for about 45 minutes (or overnight).

2. Roll out the chilled dough on a floured surface to a size that is slightly larger than a 9 inches (23cm) pie dish, transfer to the dish and press down on the bottom and sides. Fold in and straighten the dough at the edges and create a pattern with your fingers (or use a fork). Prick the dough several times (with a fork) and place in the fridge for another 20 minutes or so.

3. Preheat the oven to 390°F (200°C). For the filling add the xylitol (or sugar), butter, and cornstarch to a large bowl and mix on high until light and fluffy. Add the eggs one after another and mix well after each addition. Add the vanilla extract, lemon zest, and salt and mix until well combined. Add the buttermilk last and mix until well combined – the batter will be quite liquid now. Pour into the prepared pie crust and place it on a rack in the lower third of the oven. Bake for 10 minutes, then lower the temperature of the oven to 350°F (180°C) and continue baking for about 40-45 minutes. The filling should have set around the edges but the center is still slightly wobbly if you move the pie dish. Take out of the oven and let cool down completely.