First, put your pasta on to boil, and cook as per packet instructions
Make a roux with the lard and flour. Add the hot stock in about 4 goes.
Between each addition of stock stir the mixture until all the liquid incorporates into the flour and lard. (If you lift the pan off the heat and beat hard with a wooden spoon after the liquid is incorporated your sauce will be beautifully glossy).
By the time all the liquid is added you should have a sauce which will coat the back of a spoon. If not add more water or stock.
Stir in the mustard and most of the cheese. Leave a spoonful of cheese for the top.
Fry finely chopped bacon. Add cooked bacon to the sauce and season sauce with pepper and salt. Stir sauce into cooked pasta.
Put saucy pasta in baking dish.
Top with remaining cheese.
Cook in oven at 180 degrees until there are nice brown crunchy bits on the top.
The salt value excludes any you have added yourself, as each family's tastes will differ