Came across this Italian crockpot dish of mussels, rice, and potatoes a long time ago. They locally call the dish Tiella Pugliese in some provinces of Italy. Nothing too fancy really. It's essentially steaming those three main components in a single pot.
Recently thought of trying a slow cooker version of it, and as you will see, my efforts came out successful. Let me talk you through the process.
Start with fresh mussels of course. Fresh mussels should not stink even so slightly and should have their shells shut tight. Discard any pieces that already have open shells.
As soon as you get home, get them to soak for a few minutes in a bowl of fresh cold water. This will help get rid of any sediments that may still be in those shells.
Start working on your potatoes. Peel them and cut them into discs about a quarter of an inch thick. Cutting them this thin would make them cook at the same time as your rice and mussels do. Also, this disc shape will make assembling them in layers a whole lot easier as opposed to cutting them into other shapes, cubes for example.
Get a large stockpot or rondo with a good-fitting lid ready for steaming your mussels. Coat the bottom with about a tablespoon or two of olive oil, then sprinkle in some chopped shallots.
Add the mussels in, then add a cup of white wine. Bring the pot to a boil then put the cover on. Leave the mussels to steam for about 5-8 minutes, which should be just enough time to get their shells open.
Take the mussels out on a tray, reserving the liquid in the pot for later. Get most of the meat out of their shells, leaving some intact. Discard any mussels that have remained shut.
Coat the bottom and sides of your slow cooker with a little cooking spray to make sure that the rice and potatoes won't stick to the pot.
Start building your pot with a solid layer of those potato slices at the bottom.
Next, add in half of the rice called for in this recipe.
Top with a layer of mussel meat, then repeat layering with the same sequence of potatoes, rice, and mussels.
Finish the pot with a topmost layer of those mussels left in their shells.
Add in the stock that was left in the pot you've steamed the mussels in. Measure this liquid. Going by the ratio of 1.5 parts liquid to a part of uncooked rice, we'll be needing a total of 3 cups mussel stock for the 2 cups of rice called for in this recipe.
Add water, clam stock, chicken stock, or any other flavored liquid of your choice to make it up to this volume if you're left with less stock in your steaming pot.
Leave everything to steam for 1-2 hours on a high heat setting. You may want to check on the doneness of your rice after an hour and extend for a few more minutes if needed.