Cheese Banitza with Red Onions and Celery

I have been asked to write a recipe for the British-Bulgarian Society Newsletter,
so here it is:
This is a recipe, which I inherited from my mother, but had adapted through the years to include a vegetable component – Leeks or Red Onions and Celery

Ingredients:

100 gms Feta cheese;
300 gms Cottage Cheese (or more Feta);
½ a teacup of sunflower oil; more oil for the stir-frying of the vegetables;
1-2 cups of Yoghourt – as much as it takes?
3 eggs
½ of teaspoonful of soda (bicarbonate)
500 gms of filo pastry
2 red onions
½ of a stick of a small celery
75 gms of butter
Herbs – a generous teaspoonful of chubritza (winter savoury), and half of teaspoonful of fennel seeds
Some fizzy water – not sweet!

Preparation:

1 Peel, wash and cut the red onions, then cut the celery into small, thin circles and put into a frying pan with a bit of sunflower oil. Stir-fry gently, until they are half cooked and remove from cooker. Drain in a bowl.
2 In a large bowl, beat the eggs and add the sunflower oil, leaving some for the filo pastry sheets. Add the soda and the cheeses and stir together. Add the yoghourt, then add the cooled down onions and celery. If the mixture appears too thick, add more yoghourt to thin it up a bit. Add the spices.
3 By now, I assume you have defrosted the Filo Pasty – you open the packet now and spread the leaves on a surface. Use the plastic sheet for preparation – take two leaves together and place them of your working table.
4 On the side, you have placed in a cup the cooled down oil from the vegetables and the left over one from the previous process. Oil the bottom and the sides of your cooking tray with a sheet of kitchen towel. Cut the sheets to fit the form of the bottom, if necessary and place them to cover it fully –they can also cover some of the side walls of the dish. With a brush gently add oil here and there on the top sheet, then place 2-3 spoonfuls of the mixture on top, spread around. Then add the next layer of sheets and repeat the process, until you use all the mixture and all the Filo Pastry. The last sheet needs to be whole, not bitty. With a sharp knife cut into it vertical and horizontal lines, to form the pieces, as you will be cutting the Banitza when it is ready.
5 Turn your oven on to 200 C and allow it to warm up. In the meanwhile, put a bit of fizzy water in the bowl, where you kept the mixture and swirl it around to collect all bits remaining there and pour it over the tray.
6 Cut the butter into small bits and distribute on the surface of the Banitza.
7 Place in the oven, check after 20 minutes, if the top looks dark, place a tray to keep it from burning. Test every 10 minutes until ready.

Good appetite!