Start by melting butter in a saucepan. Once melted, add in the leeks, garlic, sage, and thyme. Continue to sauté everything together for around 10 minutes over a medium heat, until the leeks are just starting to caramelise

Then add in the flour and whisk for around a minute to incorporate. It will very quickly form a thick paste with the leeks

Then gradually add the milk in 4 increments, whisking well between each addition to ensure no lumps remain. Make sure to whisk thoroughly to prevent lumps forming

Once the last bit of milk has been added, continue whisking until the béchamel sauce starts to thicken. Alternate between a spatula and a whisk to ensure nothing is sticking to the bottom and burning. The sauce will thicken within 5-10 minutes of cooking

At this point, reduce the heat to the lowest and add in the grated cheeses. Whisk continuously until the cheeses are completely melted into the sauce

The sauce should now be slightly thick, creamy, and cheesy. Remove the thyme stems at this point (the leaves will have fallen off)

Finish the mac and cheese sauce with black pepper, nutmeg, and a pinch of salt (the cheeses already add seasoning)

For the spinach and ricotta filling, start by blanching the spinach in boiling water for 30 seconds. Then immediately strain out (blanching is a very quick process)

Transfer the spinach to a bowl full of ice cold water - this halts the cooking process to prevent them overcooking

Then squeeze the spinach to remove as much moisture as possible

Roughly chop the spinach and add to a bowl along with the ricotta, pecorino, nutmeg, salt, and pepper

Mix the spinach and ricotta mixture until combined, then set aside

Toast the sage in olive oil in a small pan over a medium heat for around 1 minute

Then pour on top of the breadcrumbs. Mix the breadcrumbs together well to coat them all in the oil evenly

Preheat the oven to 200'C (fan)/220'C (conventional) - 390'F/430'F

Boil the macaroni 1 minute under. Drain and transfer to a large mixing bowl, then pour on all of the cheese sauce. Mix the two together well

Add half of the mac and cheese to a 31cmx20cmx7cm/12"x8"x3" baking tray, and then dollop over ⅔rd of the spinach and ricotta mixture

Add the rest of the mac and cheese on top, followed by the remaining spinach and ricotta

Top the mac and cheese with the breadcrumbs in an even layer

Place the mac and cheese in the oven and bake for 10 minutes, then finish under the grill till golden brown on top (if needed)