Peel the onions and blanch them in salted water for 10 minutes. Drain them and pat dry.

Chop the cherry tomatoes into small pieces.

When the onions are cool enough to handle, cut the top off of each onion. Set the lids aside.

Use a sharp paring knife to scoop out the insides of each onion. You should have no

more than 2 onion layers remaining. If both are very thick, remove one. Chop the scooped out onion flesh into small pieces.

In a separate bowl, place a quarter cup of the chopped onion, chopped cherry tomatoes, the ground beef, ground pork, chopped fresh parsley, the beaten egg, breadcrumbs, the grated Swiss cheese, garlic powder, and thyme. Mix everything together with your hands or a large spoon until all the ingredients are evenly combined.

Season the mixture with kosher salt and freshly ground black pepper and mix again.

Preheat the oven to 350 degrees F.

Coat a large casserole dish with vegetable oil.

Working with one onion shell at a time, fill the onion shells with the meat mixture and place them in the oiled casserole dish. Cover each onion with the reserved previous cut lids.

In a separate bowl, mix together the rest of the onion pieces, vegetable broth, and dark beer. Season with kosher salt and freshly ground black pepper.

Pour the vegetable broth, beer mixture over the stuffed onions in the casserole dish. Place the casserole dish in the oven and bake for 45 minutes until the onions are cooked through.

To brown the tops of the onions, remove the casserole dish from the oven after 35 minutes.

Use a small pastry brush to coat the tops of the onions with canola or vegetable oil. Place the casserole dish back in the oven and bake for the remaining 10 minutes.

Remove from oven. Push the onion lids off to the side. Use a large spoon or a baster to pour the sauce from the casserole dish over the onions. Replace the lids and serve. 

Alternatively, transfer the stuffed onions to a serving platter, remove the lids, pour the sauce over the top, replace the lids and serve.