Cook the pasta in a large pot of salted boiling water until al dente, about 7-8 minutes. Reserve a cup of pasta water, drain, and set aside.

In the same pot, melt 2 tablespoons of butter over medium heat. Add flour and whisk for 1-2 minutes until golden.

Pour in the heavy cream gradually, whisking to combine. Cook for 3-4 minutes until thickened.

Add Boursin cheese and white cheddar, mixing until fully melted.

Fold in the cooked macaroni, stirring to combine and heat for 1-2 minutes.

In a skillet, melt the remaining 2 tablespoons of butter and toast the breadcrumbs for 3-4 minutes until golden.

Transfer the mac and cheese to a serving dish and sprinkle the toasted breadcrumbs on top before serving.