In a large bowl, mix the breadcrumbs and milk together and let sit for 5 minutes.

Add the remaining ingredients to the bowl and mix gently until combined.

With your hands, roll ~1 1/2 inch meatballs (makes roughly 15-18) and set them on a parchment paper lined baking sheet.

Heat a large pan or pot to medium heat and add the olive oil, onions, water, and salt, then mix to coat. Cover with a lid and cook for 15 minutes.

Remove the lid and continue to cook, stirring occasionally. Add a splash of water if necessary to avoid burning.

Heat a large oven-safe frying pan to medium heat with olive oil poured to coat. Once hot, fry the meatballs until browned (about 3 minutes per side) then remove and set aside.

Preheat oven to 450°F and set the rack on the middle level.

Pour off the oil used to fry the meatballs and add all of the onions to the pan along with the butter. Cook the onions until deeply caramelized, stirring frequently.

Add the garlic and cook for 1 minute. Add the flour and cook for 1-2 minutes until no longer white.

Add the wine and bring to a boil, scraping the bottom of the pan to dislodge brown bits.

Once boiling, add the chicken stock and thyme, simmer for 5 minutes. Adjust salt and pepper. Add brandy or sherry if using.

Add all of the meatballs to the pan and top with 3/4 of the Swiss cheese, bake for 7-10 minutes or until bubbly.

Top baguette slices with remaining cheese and broil for a minute to toast and melt cheese.

For a browner top, broil the meatballs for 2-3 minutes but watch carefully. Garnish with thyme leaves and serve with toasted baguette slices.