Put the stock in a large pan, bring to the
boil, then add the potatoes and the leeks. Bring back to the boil for 5 mins,
then drain well, reserving the stock in a jug.
Meanwhile, butter a large baking dish. Layer
up the potatoes and leeks higgledypiggledy, seasoning as you go, then scatter
the bacon over the top. Season well, pour over 200ml of the reserved stock and cover with foil.
Can be made up to 1 day ahead and chilled.
Bake for 40 mins, uncovering halfway through
so that the bacon crisps.