In a large bowl, combine the meat, seasonings, onion, and a tablespoon of oil. Mix well until integrated.
In a small pot, combine butter and mineral water. Heat on low until butter melts.
Grease the pan, and layer two or three sheets of phyllo on the bottom, greasing each lightly with butter and oil mixture. If your phyllo sheets are larger than the pan, cut them to fit the pan. (You can 'play Tetris' with the dough here a bit. One phyllo sheet may end up being more than one layer.) Heat oven to 480°F (250°C).
Take two, three handfuls of the filling and spread it over the top phyllo sheet in small chunks. Add another one to two layers of phyllo on top of the filling, again greasing each with butter and oil. Then add another couple of handfuls of the filling on top of the phyllo. Repeat until you are out of ingredients. (Reserve 2-3 layers of phyllo for the top.)
Layer the final layers, greasing each with butter and oil. If you can, make the top layer be in one piece. (For example, you can put a whole phyllo sheet on top and tuck the ends in on the sides.)
Bake for 5-10 minutes, or until the pie blushes. Lower to 390°F(200°), and bake 20-30 minutes. Rotate the pan once or twice during baking, and cover with foil or baking paper if it's blushing too much.
Turn the oven off, and spray the top of the pie with melted butter. Leave in the warm oven for a few more minutes. (If the phyllo blushed too much during baking, you can remove the top phyllo layer and discard, and then spray with butter)
Serving. Let the pie cool for at least 15 minutes. Serve with yogurt and a salad.Storing. If planning to store burek, it's best to keep the remaining pie in one piece rather than cutting it up. Store it in the oven for up to a day or in the fridge for up to 3. Reheating. Reheat using your preferred method, or eat cold if you prefer.