Boil water, add potato, leeks and carrot until tender.

Drain, Reserve a cup of its water, set the oven for 375

Put veggies into baking dish

A small sauce pan heat oil, add flour stir preventing get it thickens

Then add milk

Stir, add leek water

Stir until thickens and pour over leek mix

Add cheese, put it into oven, cook until cheese melts. Since veggies already cooked before, you can just wait 10 mins and turn broiler for give the cheese a good color.

Your dish is ready to be eaten.