Cook the macaroni in a large saucepan of boiling salted water for the time highlighted on the pack, then drain and set aside while you start to make your sauce.
Melt butter over a medium heat in a saucepan, then add flour and stir to form a roux, cooking for a few minutes. Gradually whisk in the milk, a little at a time, then add garlic and dijon mustard before you cook for 10–15 minutes to make a thick and smooth sauce.
Now’s a good time to preheat your grill!
Remove the sauce from the hob, add 300g of the cheese and stir until it’s mixed together. When the cheese is melted add the macaroni from earlier to the sauce, and stir through two tablespoons of Guinness Cooking Paste along with a good pinch of salt & black pepper.
Spoon the pasta and cheese mixture into an oven bake dish and top with the remaining cheese.
Mix together panko breadcrumbs, salt and melted butter to make a crunchy topping for an extra layer of bite and cover the top of the pasta.
Place under a hot grill and cook until the cheese and breadcrumbs are browned, a little crispy and bubbling, then serve straightaway (because who’d want to wait?!)