2 tbsp egg replacer (we use Ener-G for recipes like quiches that need particular help setting; as brands vary, follow pack instructions)
2 tsp plain flour
300ml double cream
4 tbsp milk
85g mature cheddar, grated
Either by hand or in a food processor, mix the flour, butter, cheese and pepper with enough cold water to combine, then knead lightly until smooth. Roll out the pastry and line a 23cm loosebottomed tart tin. Cover with cling film and chill for 30 mins. Any leftover pastry can be frozen for up to 1 month.
Heat oven to 200C/180C fan/gas 6. Remove cling film, line with greaseproof paper, fill with baking beans and bake for 15 mins until the sides are crisp. Remove beans and paper, then return pastry to the oven and cook for another 5-10 mins until lightly golden. Cool.
To make the filling, heat oil in a pan. Cook the onion until soft and the bacon until browned. Scatter over the pastry base, discarding excess fat, followed by half the cheese. Whisk the egg-free substitute, flour, cream and milk together and pour into case. Scatter remaining cheese on top.
Lower the oven to 150C/130C fan/ gas 2 and bake the quiche for 35-40 mins, or until the filling is set and the top brown. Stand for 10 mins before removing from the tin.