Mix the mayo, sour cream, mustard and egg in a mixing bowl until mixed together.
Gently fold in the crab until just combined. Shape the mixture into patties and place on baking sheet.
Bake the crab cakes for 15 minutes or until lightly golden. Run a spatula under them once or twice to make sure they're not sticking. Place them under the broiler for a minute or so until golden brown.
Place in the top of a double boiler or in a large stainless-steel bowl set up as a double boiler.
Off the heat, whisk the egg mixture until it becomes light and frothy. Place the top of the double boiler or the bowl over, not in, barely simmering water and continue to whisk until the eggs are thickened, 2 to 4 minutes, being careful not to let the eggs get too hot.
Remove the pan or bowl from over the water and whisk to slightly cool the mixture. Whisking constantly, very slowly add butter, then whisk in lemon juice, pepper sauce and salt and pepper.
If the sauce is too thick, whisk in a few drops of warm water. Serve immediately or keep the sauce warm for up to 30 minutes by placing the bowl in water (not hot) water.
Assemble with muffin on bottom, top with the crab cake and then the poached egg, finish with the hollandaise sauce.