Place milk and crabmeat in a glass bowl and cover it stretch film. Refrigerate it for 20 minutes.
Place panko bread crumbs in a 12-inch non-stick skillet and cook for 6-8 minutes, stirring constantly, until they are golden brown. Place it in a shallow plate; season it with 1/2 teaspoon salt and 1/4 teaspoon black pepper. Set aside to cool.
Wipe out the skillet with paper towel. No need to wash.
Pulse celery ribs, onion, garlic in a food processor until they are finely chopped, 8-10 pulses.
Rinse the processor bowl and blade. Set aside.
Place the butter in the skillet. Add the vegetables and season them with 1/2 teaspoon salt and 1/4 teaspoon black pepper. Cook it until all the moisture is evaporated for 6 – 7 minutes. Put them in a large bowl (this is the bowl you will get everything mixed at the end) and set aside to cool.
Wipe out the skillet with paper towel, one more time.
Strain the crabmeat through a strainer, pressing firmly to remove the milk using the back of a spatula. Be gentle not to break the lumps of the crabmeat.
Place the shrimp in food processer and pulse until finely ground, 10-12 pulses. Add heavy cream and pulse to mix, 3-4 times.
Transfer the shrimp mixture to the cooled vegetable puree. Add mustard, hot pepper sauce, lemon juice and Old Bay seasoning and mix until combined.
Add the crabmeat in and fold in gently, being careful not to break the lumps.
Divide it into 8 equal balls and firmly press them into small patties in the palm of your hands. Place each cake on a baking sheet lined with parchment paper. Cover tightly with stretch film and refrigerate for at least 30 minutes up to 24 hours.
Coat each cake with panko breadcrumbs, firmly pressing to stick the crumbs into the exterior of the cake.
Heat 1 tablespoon of oil in now-empty non-stick skillet, in medium heat, until it is shimmering. Place 4 cakes and cook without moving until they are golden brown, 3-4 minutes. Using two spatulas flip them. Add one tablespoon of oil and cook the other side for 2-3 minutes. Place them on a platter.
Wipe out the skillet with paper towel and repeat the same process for the rest of the crab cakes.