Mix the water and cucumber slices in a pitcher. Refrigerate until ready to serve.

Prep the soup ingredients per the instructions above.

Begin caramelizing the onions with olive oil and butter:

In a thick-bottomed pot, heat olive oil on medium heat. Add the onions and toss to coat with the olive oil. Cook the onions, stirring often, until they have softened, about 15 to 20 minutes.

Increase the heat to medium-high. Add the butter and cook, stirring often, until the onions start to brown, about 20 to 40 minutes.

(The amount of time will vary depending on your pot, stove, and onions.)

Sprinkle onions with sugar (to help with the caramelization) and salt. Continue to cook until the onions are well browned, about 10 to 15 more minutes. Add the minced garlic and cook for a minute more.

Deglaze the pot with wine and scrape up the browned bits on the bottom and sides of the pot, deglazing the pot as you go.

Add the broth, bay leaves, and thyme. Bring to a simmer, cover the pot, and lower the heat to maintain a low simmer. Cook for about 30 minutes.

While the soup is simmering, line a sheet pan with parchment paper or foil and preheat the oven broiler on low.

Brush both sides of the French bread lightly with olive oil. Toast until lightly browned, about 5 to 7 minutes. Remove from the oven.

Turn the toast over and sprinkle with the grated Gruyere cheese and Parmesan. Return to the oven when it's close to serving time and bake until the cheese is bubbly and lightly browned.

Season to taste with more salt and pepper. Discard the bay leaves. Add brandy if using.

To serve, ladle soup into a bowl and transfer one cheesy toast onto the top of each bowl of soup.

(Alternatively, you can use individual oven-proof bowls or one large casserole dish. Ladle the soup into the bowls or casserole dish. Cover with the toast and sprinkle with cheese. Put into the broiler for 10 minutes, or until the cheese bubbles and is slightly browned.)

Prep the brie crostini: Drizzle the crostini with oil, place sliced brie on each crostini, then drizzle with honey. Broil until the cheese is melted and the crostini edges are golden brown.

Serve the soup with brie crostini and cucumber water.