For the broth: Heat the oil in a medium pot over medium-high heat. Add the shrimp heads and shells and saute a few minutes until starting to brown. Add the celery, bay leaf, leeks, onions and peppercorns; stir for a couple of minutes. Add the herb bundle and cover with the stock, then add the saffron and bring to a simmer. Let bubble gently for about 30 minutes. Strain and reserve.
For the spicy garlic aioli: Whisk together the egg yolk, garlic, Dijon and lemon juice in a small bowl. Whisking constantly, slowly stream in the oil to emulsify. Season with salt, pepper and hot sauce.
For the bouillabaisse: Heat 1 tablespoon of the oil in a medium to large Dutch oven over medium-high heat. Add the andouille and cook until browned and crisp. Remove from the pan and set aside.
Reduce the heat to medium and add the remaining tablespoon olive oil to the Dutch oven. Add the garlic, celery, onions, fennel and bell peppers. Let sweat for 8 to 10 minutes, adding the tomatoes during the last few minutes of cooking. Raise the heat to medium-high, add the beer and bring to a simmer. Let reduce for a few minutes, then add 2 to 3 cups of the shrimp stock and bring to a simmer. Add the redfish and shrimp and let cook through, 3 to 4 minutes. Remove from the heat and stir in the crabmeat to heat through. Season with Old Bay and hot sauce and add the andouille back to the pot.
To serve: Spread the aioli on the toasted baguette slices and divide among four shallow bowls. To each bowl, add three pieces of fish, three pieces of shrimp, some crab and some Andouille. Pour in some of the broth, making sure to include the vegetables in the broth. Garnish with the reserved fennel fronds.