If you don't want to use a bag, toast the halves separately on an oven rack, buttered sides up, until golden. Using salted butter saves seasoning the bread, but you can use unsalted butter and a large pinch of salt.
How to Make the Ultimate Umami-Bomb Vegetarian Demi-Glace
1 large garlic clove, minced
2 tablespoons salted butter, softened
1 loaf of Italian bread, preferably semolina, halved lengthwise
2 tablespoons freshly grated Parmesan cheese
Preheat the oven to 450°. In a small bowl, blend the garlic with the butter. Spread each bread half with 1 tablespoon of the garlic butter and sprinkle with 1 tablespoon of the Parmesan. Sandwich the bread halves together and put the loaf in a paper bag. Fold the top closed and bake in the center of the oven for about 8 minutes, or until the bag darkens slightly and the bread feels crisp when pressed through the bag