Melt the butter in a small skillet over medium heat. Add the onions and wine or stock. Cook, stirring occasionally, until the onions begin to caramelize. Add the minced garlic about halfway through the cooking. Cook for about 10 minutes altogether. Scoop out of the pan, but do not wash the pan. Cut your panini roll in half horizontally. Spread the caramelized onions on the bottom half of the roll. Sprinkle with the dry onion soup mix and the Parmesan Cheese. Cover with the gruyere and then the croutons, crushed. Top with the top half of the bun. Heat the skillet and place the panini into it top side down first. Weight down with a saucepan that you have a heavy tin inside. Cook for several minutes and then flip over and replace the pan on top and cook for a few minutes longer, until golden brown and the cheese is melted and gooey. Cut on the diagonal and serve.