Bring a large pot of salted water to a boil and cook the macaroni slightly under al dente. Drain and reserve some pasta water for later use.

In a skillet, heat butter and olive oil. Cook the shrimp for a few minutes until just pink, then remove and set aside to avoid overcooking.

In the same pan, melt butter and whisk in flour. Cook until it forms a smooth, light golden paste with a slightly nutty aroma.

Gradually add milk and cream while whisking continuously. Let the mixture thicken before adding the cheeses in batches, stirring until smooth.

Add the lobster and shrimp to the sauce, then fold in the cooked pasta. Adjust the texture using reserved pasta water if needed.

Transfer to a baking dish and bake until the top is golden and bubbling. Let it rest before serving for the best consistency.