To make this Mushroom Bouchees Recipe gluten-free, replace the white sandwich bread with certified gluten-free sandwich bread that is soft enough to roll without cracking. Confirm that the canned mushroom pieces, cornstarch, half and half, butter, green onions, garlic, salt, and black pepper are gluten-free and free from cross-contact. If the gluten-free bread is firmer than regular sandwich bread, warm it slightly before rolling or choose a softer brand for better flexibility. Use clean utensils, a clean rolling pin, and a separate baking sheet or parchment paper to prevent cross-contamination.