Preheat the oven to 200C/400F (180C/360F fan) and place a baking sheet on the centre shelf.
Now, make the pastry. Tip the flours into a blender with the salt and pepper. Cube the butter and add to the processor. Pulse until the mix resembles a coarse crumb. Add the eggs one at a time. Pulsing in short bursts until it comes together. Remove from the processor and knead into a smooth ball. If the dough is sticky, knead with a little flour. Wrap in cling film and place in the fridge.
Now start making the filling. Melt the butter with the garlic until bubbling gently. Add the spinach and fry gently until wilted.
Slice the mushrooms and add to the pan with the oregano, salt and pepper. Fry until the mushrooms are pale golden. Then set aside to cool.
In a jug, measure the milk and add the eggs. Beat well until completely combined.
Turn out the chilled pastry on to a floured surface. Roll into a disc large enough to cover your quiche case with a little overhang. Drape the pastry gently over the tin, then use the pads of your fingers to gently press the pastry into the edges of the tin. Gently prick all over the bottom and sides with a fork.
Line with paper and baking beans and bake gently for 10 minutes until lightly dried out. Remove paper and beans and carefully trim off the excess pastry with a sharp knife.
Spread the spinach and mushroom mix on the bottom of the case. Scatter the feta on top.
Pour on the egg mix, but stop a half inch from the top. This will make it easier to carry to the oven. Once the quiche is on the oven shelf, add the last bit of egg mix until the case looks almost full, then bake for 40-50 minutes until golden.
Chestnut mushroom, spinach and feta quiche https://www.amummytoo.co.uk/chestnut-mushroom-spinach-feta-quiche/