Add potatoes to a large pot of water and boil until tender but a little firm (we will be baking them later). You should be able to stick a fork into them but it should still be a little hard.
Pre heat oven to 375° F
Carefully cut potatoes length wise and scoop out the insides using a spoon. Be careful not to break potatoes in half. Start by shallow scoops from the surface and slowly work your way to the bottom.
Place spinach, garlic, onion, black pepper, salt, old bay seasoning, and mayonaise in a food processor. Pulse 6-8 times. Add in lump crab meat and pulse another 6-8 times.
Using a spoonful at a time, carefully fill the potatoes with the crab and spinach mixture, packing it in and adding more ontop.
Place stuffed potatoes in a pan where they will be tight and can lean on eachother for support (otherwise, it will tip over and filling will fall out). Bake for approximately 30 minutes. *Note: If you don't have a pan that allows them to be close, build some walls with tinfoil instead.
While potatoes are baking, start to prepare creamy sauce by placing butter in a pan on medium heat. Once butter is melted, add gluten free flour and whisk until you form a rough. Add almond milk, chicken broth cube, and nutritional yeast and continue sitrring until sauce thickens.
Remove potatoes from oven and evenly distribute cream sauce on top of each stuffed potato. Serve when warm and enjoy!