To steam lobster, fill a medium-sized lidded pot with 1 inch of water and bring to a boil. Add the lobster tails, cover, and simmer for 8-10 minutes. Here is another post on steaming full lobster. Crack or cut the shells open with kitchen sheers and chop into bite-sized chunks. Always thaw lobster before steaming!

Preheat oven to 375 °F.

Bring a large pot of salted water to a boil. Cook elbows until al dente. Strain and set aside.

Meanwhile, spray a cast iron skillet liberally with cooking spray. Melt butter over medium-low heat. Add the flour 1 tablespoon at a time, whisking constantly until incorporated and roux has formed, about 1-2 minutes.

Slowly whisk in warm milk, one cup at a time, whisking out any lumps if they form. Heat until sauce just starts to bubble in the center. It helps to whisk constantly during this process.

Reserve 1/2 cup of cheese in a small bowl for step 6. Add half of the remaining cheese to the skillet, whisk until nearly all is melted and creamy. Add the other remaining half and whisk until smooth and creamy.

Stir in cooked elbows and lobster until evenly distributed. Evenly top with a layer of the reserved 1/2 cup of cheese and then crushed croutons.

Bake for 10 minutes or until croutons are golden. Serve immediately.