First make the pastry. Sift the flours and salt into a large mixing bowl. Add the butter and lightly rub it into the flour until the mix looks like fine breadcrumbs. Gently fold in the chives and grated cheddar. Sprinkle over the cold water and stir it into the pastry along with the beaten egg. Bring the mixture together to form a green-flecked dough and shape it into a ball, leaving the bowl clean.
Roll out the pastry into a rectangle and use it to line a butter-greased, shallow baking tray or tart tin (about 35cmx25cm). Prick the base with a fork a few times, then put in the fridge to chill for at least 30 minutes.
Lightly beat the goose eggs in a jug. Remove the pastry from the fridge and brush the inside with some of the beaten egg, before popping it in the oven and baking for 15 minutes until lightly cooked and dry to the touch. If it puffs up a little during cooking, lightly prick it with a fork again and gently push down to deflate it (we learnt this tip for blind baking without beans from Delia Smith's website).
Bring a deep-sided pan of water to the boil and drop in the nettles. Simmer for a few minutes until they are wilted and are cooked through. Drain and leave to cool before squeezing out any excess water from the leaves. Reuse the same pan to melt a generous knob of butter over a medium heat, add the dandelion leaves and cook for a couple of minutes before throwing in the wild garlic leaves, which will wilt almost immediately. Once the dandelion and wild garlic leaves are cooked, stir in the drained nettles and season with salt and pepper.
Scatter the cooked greens evenly over the base of the pastry case, then sprinkle over the grated cheddar and pour over the egg mixture. Bake in the oven for 30-40 minutes until puffed up, cooked through and blistered golden.