Let Brie sit at room temperature to soften.
In a bowl, mix butter, chives, parsley, Dijon mustard, and grated garlic. Season with salt and pepper.
Toss arugula with lemon juice. Season with salt and pepper.
Spread the herb butter evenly on the bottom half of the baguette.
Layer with ham, Brie, and season with salt and pepper. Top with arugula and cover with the top half of the baguette.
In a pitcher, mix lemon juice, water, and sugar. Stir until the sugar dissolves. Serve over ice if desired.
Enjoy the jambon beurre with chips, a pickle, and fresh lemonade.