Cover shrimp with water in a large saucepan. Add shrimp boil. Bring to a rolling boil and cook 2 minutes. Turn off heat. Let shrimp sit in liquid until they are pink and mostly opaque, at least 15 minutes.

Set a large sieve or colander over a big bowl and drain shrimp, saving the shrimp stock.

In a large heavy-bottomed pot, melt butter and saute onion, bell pepper and celery until translucent, 6 to 8 minutes. Add beans and enough of the shrimp stock to just cover them. (If you have shrimp stock left over, freeze for another use.)  Season well with salt and pepper. Bring to a boil over high heat, then lower to a simmer. Cover but leave the lid ajar. Cook 15 minutes.

Use a potato masher to mash some of the beans, for thickening. Add shrimp. Stir well. Cook 5 minutes.

While that's cooking, in a small skillet, melt 1 tablespoon butter with olive oil. Add flour and stir well to make a white sauce/roux. Cook just until the mixture starts to brown and smells toasty, stirring occasionally.

Stir into the simmering bean and shrimp mixture. Taste and adjust seasoning, adding hot sauce and Creole seasoning. Cook over low heat another 5 minutes, then serve warm over rice.