Mix together the cold butter and plain flour. Rub into a crumb consistency. Keep mixing until combined into a ball.
Roll this out and use it to line a fluted quiche tin. I rolled the shape larger than my tin and used my rolling pin to place it over the top of the tin. Then I used a small piece of dough to press the rolled dough into the tin thoroughly.
Place in the freezer for 15 minutes to firm up.
Place 500g of onions, and butter, into a saucepan. Stir regularly and cook for around 10 minutes. This makes a consistency that is still crunchy, with a nice bite but makes sure that the onions aren't overcooked.
Line the cooled pastry in the tin with foil and then pour in baking beans.
Bake at 200C (gas mark 6) for 15 minutes.
Remove the baking beans and bake for 5 more minutes until the pastry is lightly browned.
Whisk together the eggs and combine with the double cream.
Add seasoning (salt & pepper) then add the onions and grated cheddar.
Pour this mixture into the pastry case.
Top with black pepper, grated cheddar and one finely chopped green chilli if you like a little heat.
Place bake in the oven, at 200C (gas mark 6) for 30-35 minutes.