• Preheat the oven to 375 F.

Pie crust

• In a medium bowl, combine the flour, sugar, and salt. Add the cubed butter into the dry mixture and rub the butter cubes between your fingers into pea-sized pieces.
• Add the apple cider vinegar and water into the mixture and gently mix together. If needed, add an extra 1 tsp of water at a time until the right consistency is achieved. The dough shouldn’t be too sticky or too dry. Once the dough is formed, wrap it in plastic wrap and put it in the fridge while you make the filling.

Filling

• Heat a frying pan with the olive oil. Once heated, add the chopped onions and mushrooms. Fry the vegetables until they are browned and softened, about 2-3 minutes. With the fried onions and mushrooms still in the pan, add the chopped turkey and fry for 1-2 minutes. Remove from the pan and let the mixture cool.
• Whisk together eggs, heavy cream, milk, salt, and pepper in a medium bowl. Add the cubed cheese and the turkey mixture, stir, then set aside.

Assembling and baking

• Remove the dough from the fridge, unwrap it, and dust your surface with flour. Roll out the dough about an ⅛ inch thick, then press the rolled-out dough into an 8-inch (bottom) and 10-inch (top) circle pan (leave about 1 inch of dough hanging off the sides of the pan because it will shrink).
• Pour the filling into the pan lined with dough and place it on a metal baking tray.
• Place it in the preheated oven and bake for about 50 minutes or until the crust is browned and the filling is set.
• Remove the quiche from the oven and let it cool for 15 minutes before serving, or let it cool completely, then refrigerate for 3-4 days, or freeze for longer (2-4 months) storage.