Rinse potatoes under cold running water, and let soak in a bowl for a minimum of 1 hour.

Using a sharp knife, hand-cut fries lengthwise, 1/2 inch (1 cm) in width. Fill a clean sink basin or very large bowl with cold water, and submerge cut fries, rinsing off any excess starch. Transfer fries to paper towel to absorb excess moisture. Pat dry with paper towel to remove additional moisture, and set aside at room temperature.

In a large, heavy-bottomed pot, heat 8 cups (2 L) of oil to 350°F (180°C).

To cook the fries, work in batches, placing fries in hot oil and cooking for 5 minutes or until cooked through and soft, but not crispy. Using a spider or slotted spoon, remove fries from the pot and transfer to paper towel to absorb excess oil. Repeat this process until all fries are cooked. Set cooked fries aside at room temperature, reserving the oil. Turn off heat until ready to serve.

Bring a pot of water to a boil over high heat. Remove the core from two tomatoes, and score the skin on the opposite end with a paring knife. Place the tomatoes in boiling water for 10 seconds. Turn off heat, carefully remove tomatoes from pot with a sieve and rinse under cold running water until chilled, approximately 2 minutes. Peel the skin from the chilled tomatoes, and cut in quarters lengthwise. Remove the seeds, and finely dice the tomatoes. Set aside.

Remove the beard from each mussel by firmly pulling on the small stringy tag where the mussel shells meet. Rinse the mussels under cold running water, and scrub gently to remove any excess grit. Set aside.

Return oil in pot to 350°F (180°C), ready for frying the fries as soon as the mussels are cooked.

In a separate large pot, heat 1 Tbsp (30 mL) of oil over high heat. Add onion, and stir while frying for 4 minutes or until onion begins to catch and slightly brown. Deglaze the pot with beer, scratching any caramelized bits of onion from the bottom of the pot with a wooden spoon. Add mussels, cover with a lid, and bring beer stock to a boil. Cook mussels for 5 minutes or until it looks like all mussel shells have open. Discard any unopened mussels. Remove mussels from heat, and use a slotted spoon to transfer the mussels from the beer stock to serving bowls, leaving the cooking liquid in the pot.

Return fries to the hot oil for final cooking process, and cook in batches for 3 minutes or until crispy and golden brown, approximately 3 minutes.

While fries are cooking, return the beer stock to high heat. Add tomatoes and chermoula, stir to combine, and bring to a boil. Add cream, and stir to combine. Season with salt and pepper, and reduce for approximately 2 minutes while fries finish cooking. Remove sauce from heat, and set aside at room temperature.

Transfer fries from the pot to a large bowl lined with paper towel. Season with salt, tossing fries to coat evenly.

To serve, ladle even portions of sauce over the mussels in each serving bowl, and garnish with cilantro. Serve with fries, lemon wedges, and aioli on the side.