In a medium saucepan, cook the macaroni until it is al dente, about 6 to 8 minutes (usually a little less time than is in the instructions on the package).
Drain and set aside.
In a large saucepan, melt the butter in the saucepan over medium heat.
Add the chopped onion and saute until softened, about 2 minutes.
Stir in the flour and cook for 2 - 3 minutes, whisking constantly.
Gradually add the chicken broth and milk in alternate batches.
Bring the sauce to a boil, whisking constantly.
Add the tabasco.
Remove from the heat.
Add half the cheese (about 3 cups) to the sauce and stir until it melts.
Stir the cooked macaroni pasta into the cheese mixture.
Pour half of the macaroni and cheese sauce mixture into the crock pot.
Sprinkle half of the remaining grated cheese over the macaroni.
Pour the rest of the macaroni and cheese sauce into the crock pot.
Sprinkle the rest of the grated cheese over the top.
At this point, you can store the dish in the refrigerator for up to 2 days or freeze it for up to a month. If you freeze it, take it out of the freezer the night before so that it thaws before you cook it.
To cook, cover the crock pot and cook on low heat for about 2 hours.
Don't use pre-grated cheese. It contains additives that prevent it from sticking to the package which also affect its consistency when it is cooked.
The macaroni and cheese can be left in the crock pot on the warm setting for 2 to 3 hours after it has finished cooking.