Add the flour, cubed butter and salt to the bowl of a food processor and pulse until a sandy texture forms (about 30-40 seconds).
Add the eggs all at once and pulse until the whole mixture begins to clump together (another 30 seconds). The mixture should stick together and hold it's shape when pressed between your fingers. If it doesn't, add a tablespoon of water and pulse again. Repeat once more if necessary to get the right texture.
Turn the mixture out on your work surface and use your hands to bring it all together into a ball. Cover and put in fridge until ready to roll out.
prepare the filling
Preheat oven to 180 C / 355 F.
Finely dice the carrot and celery. Mince or mash the garlic clove.
Add the butter, onion, celery, carrot and garlic to a skillet with all the seasonings and half the salt and pepper. Sauté until aromatic and well reduced (about 8 minutes).
Turn off heat and pour in the water.
Allow the mixture to cool while you grate or finely dice the potato and then add the potato to the skillet.
Mix the ground meat in until the mixture is homogenous. Set aside until you're ready to fill the pie dough.
rolling out the pie dough
Cut the dough into two pieces and roll each piece out to about half a centimeter or a little more than ⅛ of an inch thick.
Use your springform pan as a guide to cut out a top and a bottom round.
Reroll the remaining pie dough. Use a knife to cut out strips to line the pan. They should be about 8cm/3 inches tall and go all around the pan (so a total length of 75 cm / 30 inches for a 24 cm / 9.5 inch pan).
Prepare the pan by rubbing all over with butter and sprinkling liberally with flour - then tap out the excess.
Put the bottom of the dough into the pie pan and then line the sides of the pan with the strips. It's okay if you have to stick a few together or fill in any gaps. Be gentle and use the back of a teaspoon to smooth the pieces together.
final assembly and bake
Fill the prepared pie shell with the filling and smooth it out using the back of a spoon or lightly wet fingers.
Cover the filling with the top pie round. Smooth out the top with the back of a spoon or slightly wet fingers.
Decorate the top of the pie and apply eggwash if desired.
Bake in preheated oven for 1 hour 15 minutes until golden. If the top browns too quickly, cover lightly with aluminum foil.