As to the last questions, I think using omelet and pizza notions are good starting places for fillings. When inspiration fails, admiration (i.e., borrowing) is a good road to success. The main issue is texture. The filling needs to be tender and warm without being wet, oozing, or rubbery. So those sound like good sources for ideas.

Cornflakes? No. I mean, for inventive housewivery, why not, but the crust is for holding it together and making it pretty, and shouldn't have such a strong flavor.

I wouldn't be surprised if the secret to those catering company pucks were meat glue. I think using a vacuum sealer compress the filling to make it hold together for classic stuffing might be a good thing to try. For pounded and rolled it probably doesn't make that much difference.

Good luck with your quest. Do report back on your results!

I ended up making Cordon Bleu, and I used sliced deli ham and Havarti cheese for the filling.

I pounded the two breast pieces that I was using (and froze the rest), and then smeared them with a small amount of Dijon mustard before adding the filling. Then I rolled them up tightly in plastic wrap and stored them in the fridge for 30 minutes.

Then I sprinkled them with Sazon (Spanish seasoning that has salt, chili, paprika, garlic powder, and onion powder), dipped them in melted butter and then rolled them in bread crumbs that I made myself.

I baked them in the toaster oven at 400° for 20 minutes, checked for temperature, and then put them back in for 5 minutes more.

I served them with a chicken velouté sauce that I made with butter, chicken fat, black pepper, flour, chicken stock, and a bit of Sauvignon Blanc. If I had thought of it, I would have added lemon juice, perhaps instead of the wine. Anyway, I was afraid they might be a bit dry if I did not serve a sauce.

I also boiled some Yukon gold potatoes and steamed some broccoli for side dishes. I put some of the velouté sauce on my potatoes.

My one criticism is that I might not have pounded the breasts thin enough.

I found several recipes that called for corn flakes instead of bread crumbs, but I thought that bread crumbs were perfect - I did not want to add corn flavor to it, and the bread crumbs got crunchy enough.

I want to try stuffing some with spinach and mushrooms, but I'll have to buy some spinach.. The recipes I've seen for this call for cream cheese, but I would rather not use that and maybe use Fontina instead.

Some recipes called for rolling the chicken rolls in flour, then egg, and then bread crumbs, but I found that the butter worked well enough and was much easier.

You can stuff chicken with kind of anything that can go with chicken, including regular bread stuffing :) I tend to pocket cut more than roulade. I've done creamy crab stuffing with the chicken on the grill, bread stuffing baked in the oven, gratin style laid out on a roulade- root veggies are nice for that. Some seared off fennel and carmelized onion is a nice filling braised in stock and served with some mash or a side of beets and cauliflower. Stuffed with poblanos, red onion, and oaxaca cheese- kind of a reverse chili rellenos. Stuffed with some shrimp and hominy and simmered in spicy tomato sauce- crack an egg in the sauce to poach up to serve on top. Stuff with water chestnuts and kimchi and toss into a long and slow congee pot. Apples and asparagus or apples and winter squash can be good, or a well seasoned mince of walnuts with cottage and cheddar cheese.

“I tend to pocket cut more than roulade.”

Same for me. I’ve also ”stuffed” boneless breasts with skin, but they can be hard to find. I had to order them the last time I wanted some. I’ve used them to stuff by placing an herb-y cheese mixture, like Boursin, under the skin with spinach or basil leaves.

Last stuffed chicken was very good. I think it was chicken breast pounded out. spinach, crumbled cooked bacon, garlic and goat cheese. Rolled up, Sealed with string or toothpicks, browned on all sides, then baked for????? 20 minutes? Really good, though!

Oh, and re sauces, have you tried using a plant milk for classics? Think coq au vin and do a reduction? Take the trimmings from the filling and simmer in stock or butter or wine or whatever, reduce and strain?

Do you mean "plant" milk (instead of "lant")? I see no reason to use that, as I am perfectly happy to use stock instead of any kind of milk. I sometimes use mushroom stock, if I am making a mushroom sauce. I think an avgolemono sauce would be good, if I wanted to richer tasting sauce.

Yes, plant. In some situations one or another works. Just if you wanted the sauce. If you're happy without it, no worries. ;)

That looks like a good recipe, and I could easily adapt it. I would omit the nutmeg as I hate nutmeg in spinach, but the rest of the filling looks good. It is very similar to what I use as a filling for ravioli.

I think if you're making kiev, then you need to breadcrumb it fully using the flour, egg and breadcrumb method to seal it or you risk losing all the lovely butter. I often air fry cordon bleu and that I coat just using egg, then panko. I brush them lightly with oil and they're really good. Stuffing a chicken breast is a lot of faff when often, you can put the stufing on top as a sauce LOL. One of my favourite things is to do a cheat veal schnitzel, using well bashed chicken as veal is a hefty price here. Served with the traditional toppings, (capers, lemon, anchovies....) delicious.

I haven't made the Kiev yet, although I have chicken breasts in the freezer now. I'm not sure I really want a butter filling. I thought I had had it in the past, but perhaps I have not. I did like the way the Cordon Bleu turned out, however.

I do think that the butter from Kiev could be put on top instead of inside, as you suggested, and that would make it easier to make.