1. Put the bay leaves, leek and milk in apan, and gently heat until steaming butjust below boiling point. Take off the heatand set aside to infuse for 1 hr.
2. Drain the milk and discard the leekand bay. Wipe out the pan, then add thebutter, flour and mustard powder.
3. Heat,stirring, until the butter has melted, thencook to a paste for 1 min. Splash in somemilk gradually and stir until smooth andcompletely incorporated.
4. Add the restof the milk, a little at a time at first, thengradually add more as the mixture getssaucy. (If you get any lumps, give it avigorous whisk to remove.)
5. Heat, stirringall the time and scraping the bottomof the pan so it doesn’t catch, until thesauce is bubbling and nicely thickened.
6. Remove from the heat and stir in200g of the cheddar and 25g of the
7. Parmesan. Season really well –keep tasting as it will need agenerous amount of salt.Cook the macaroni followingpack instructions, until it is almosttender but still has a bit of chew to it.
8. Drain well, then stir into the cheesesauce with three-quarters of the springonions.
9. Scrape into a large ovenproofdish or several individual ones.Scatter the remaining cheddar overthe macaroni, then alternate betweendraping over pancetta slices (bunchingthem up a bit) and scattering with thebread cubes and remaining springonions. (If you keep swapping betweeningredients you’ll get a nice mix ofeverything on the top.) Sprinkle with theremaining Parmesan and add a very littledrizzle of oil – holding your thumb overthe bottle so just a trickle comes out.Can now be cooled, covered andchilled for up to 1 day, or frozenfor up to 1 month.
10. Heat oven to 180C/160C fan/gas
11. Bake for 40 mins until bubbling, andcrunchy and golden on top (if usingindividual dishes, check after 30 mins).