Preheat your oven to 180°C (350°F).
Boil a large pot of salted water and cook the pasta until just al dente, about 8 minutes. Drain and set aside, keeping a cup of pasta water.
In a saucepan, melt the butter over medium heat, listening for it to sizzle and smell nutty.
Add the flour to the melted butter and whisk continuously for 1 minute until the mixture turns slightly golden and thickens.
Gradually pour in the milk, whisking constantly, and cook until the sauce thickens and coats the back of a spoon, about 5 minutes.
Add shredded cheddar, Gruyère, and blue cheese to the sauce, stirring until melted and smooth. This creates a rich, cheesy sauce with depth.
Stir in the cooked pasta into the cheese sauce, mixing well. If the sauce is too thick, add a splash of reserved pasta water to loosen it.
Transfer the cheesy pasta into a buttered baking dish, spreading it evenly.
Mix the breadcrumbs with olive oil and sprinkle evenly over the top of the pasta for a crispy topping.
Bake in the preheated oven for about 20 minutes, until bubbling around the edges and the breadcrumbs are golden brown.
Remove from the oven, let it sit for a few minutes, then serve hot to enjoy the creamy interior with a crunchy topping.
