1) Preheat griddle to 180 degrees C.
2) Quarter red and green pepper, then place them on the griddle, cooking until tender. Once griddle marks are formed, remove peppers from griddle and set aside.
3) Boil elbow macaroni in salted boiling water until al dente - drain and set aside.
4) In a large saucepan over medium heat, melt butter and then whisk in flour to thicken, about 1 minute. Add 250ml milk and whisk in. Begin adding cheeses 1 at a time, thoroughly whisking each cheese. If sauce becomes too thick, add remaining 250ml of milk.
5) Once all cheeses are blended add salt, black pepper, cayenne pepper, griddled peppers, jalapeno pepper and stir to combine. Add elbows to mixture and stir again.
6) Once combined well, add to a cast iron 23 by 33cm rectangle casserole dish, and sprinkle top with bread crumbs and an additional 1/2 tsp cayenne pepper.
7) Place on griddle for 12 minutes. Let stand a few minutes before serving.
8) Serve immediately.