Slice scallops into three discs and chill in the fridge.
Scrub the scallop shells and grease the insides with butter.
Preheat the oven to 220°C.
Infuse the milk with the bay leaf and onion by simmering and then standing for 15 minutes.
Strain the infused milk through a fine sieve into a jug.
Melt 30g of butter in a pan and stir in the flour and mustard powder for 30 seconds.
Gradually whisk in the infused milk until smooth.
Stir in the wine, cream, and 25g of cheese and simmer for 3-4 minutes until thick.
Remove from heat and stir in the scallops, chives, and seasoning.
Distribute the crabmeat into the shells and spoon the scallop mixture over it.
Combine breadcrumbs, 25g of cheese, and parsley to sprinkle over the seafood.
Bake the shells for 18-20 minutes until golden and bubbling.
Serve warm with a green salad and white wine.