In a large saucepot over medium-low heat, melt two tablespoons of butter, add in the onions, and season with kosher salt and pepper. Give the onions a stir and allow them to cook, stirring frequently, until softened and starting to brown slightly, about 15 minutes. Turn the heat up to medium/medium-high, add in the remaining butter, garlic, and maple syrup, and allow the onions to cook and caramelize for ten more minutes, stirring frequently. Turn the heat down to low, add in the herbs, and deglaze the pan with the brandy and balsamic vinegar, stirring very well and scraping the bottom of the pan to incorporate any of the golden bits that have developed.
Add in the Irish stout and allow it to bubble until reduced by half then stir in the beef stock and bring the mixture to a simmer. Cover the pot and allow it to cook for 25 to 30 minutes to allow the flavours to meld.
Season the soup with more salt and pepper to taste then ladle it into four oven-safe soup ramekins or French onions soup dishes. Turn the broiler on to high and top each ramekin of soup with a piece of country bread and a good scattering of Irish cheddar. Broil until lightly browned, about three to five minutes, making sure to keep your eye on it so that the cheese and toast don’t burn.
Allow to cool slightly before digging in with a pint on the side.