Place a frying pan on medium heat and pour the 1 tbsp of oil. Once it heats-up add the bacon and fry for 5’ until they get a bit of a colour, while frequently tossing them. Remove from the heat and keep aside.
For the Béchamel, place a medium non-stick pot over medium heat and melt the butter. Add the flour and cook for 2’ while whisking. Add the mustard and mix well.
Reduce the heat to low and start adding the milk, a bit at a time and keep on whisking.
Halfway through add the cream, the nutmeg, salt and pepper and continue adding the milk and keep on whisking aiming to achieve a nice, just a bit runny cream.
Then add slowly the cheddar cheese, if you add it altogether there is a chance to curdle, and whisk until smooth, moving saucepan on and off heat to keep it hot enough to melt the cheese but not so hot that it bubbles rapidly. Add the bacon into the béchamel and keep aside.
In the meantime, in a large pot bring water to a boil on high heat adding the 2 tbsp of salt. Add the macaroni, stirring occasionally so as not to stick and cook 2’ less than package instructions. Drain and return to their pot and pour in it the bechamel.
Preheat the oven to the 190°C, air circulation, rack in the middle. Take a large (~35 CM) rectangular non-stick oven dish that is deep enough (about 5 cm) and brush it with a bit of butter. Add the pasta with the béchamel and spread evenly. Mix the grated Parmigiano Reggiano cheese along with the breadcrumbs and sprinkle on top and cook for about 30’ and until you get a nice golden colour.
Take out of the oven and serve.