Be sure to fill the well all the way to the top, and be generous in how much potato you put in each well. They will shrink in volume as they cook.
Check out this vegan cheese sauce from Minimalist Baker. They key component will be how thick your sauce is. You want the cheese sauce to stick to the cauliflower as a binding agent to keep it all together. Alternatively, skip the cheese and make buffalo cauliflower bites.
You can use sweet rice flour instead of regular wheat flour to make your roux. Or skip the sauce entirely and just sprinkle some cheese on top of the cauliflower inside the potato cups and melt.
Bacon and ham are the most natural additions. My 5 year old self would request diced hotdog. Grown up me would suggest breakfast or spicy sausage. Be sure to cook your meat thoroughly before mixing together with the cheese sauce and roasted cauliflower.
Don’t have cauliflower? Broccoli, carrots, parsnips, cabbage, Brussels sprouts, or a combination of these would be great as a substitute. Or mix all the above with cauliflower. This recipe is perfect for using up any leftover raw or roasted vegetables in your fridge. Did I mention the awesomeness of cheese and roasted vegetables?
Instead of using frozen hash browns, shred russet or yukon potatoes using a box grater or food processor. Be sure to press all the moisture out of the shredded potatoes. You can use a cheese cloth, dish towel or fine mesh strainer.