Dal Baati is a Rajasthani plate, not a sandwich, and it is worth describing on its own terms. It pairs hard, baked wheat balls called baati with a pot of spiced dal, and is most often served as a trio with churma, sweet crumbled wheat sweetened with sugar or jaggery and ghee. The angle is durability: the baati is a dense, slow-baked bread designed to keep for a long time in a dry climate, eaten by breaking it open and soaking it in lentils and ghee rather than holding anything inside it.
The components are made separately and assembled at the plate. The baati dough is a stiff mix of coarse wheat flour with a little ghee and salt, rolled into balls and baked or roasted until the outside is firm and cracked and the inside is dense and crumbly; traditionally they are cooked over cow-dung cakes or in a wood oven, which gives a faint smokiness. The dal is usually a blend of lentils, simmered and finished with a tempering of ghee, cumin, garlic, and chilies. To eat it, the baati is broken into rough pieces, often drowned in warm ghee, and then either dunked into the dal or topped with it so the dense crumb soaks up the liquid and softens. Good dal baati gives a baati that is cooked through with a crisp shell and no raw doughy center, a dal with enough body and tempering to flavor the bread, and enough ghee that the dry crumb turns rich rather than choking. Sloppy versions leave the baati pale and underbaked in the middle, or serve a thin, underseasoned dal that cannot carry the bread.
Regional and household versions vary the baati itself: some are stuffed with a spiced pea or lentil filling before baking, some are made smaller and crisper, and the dal blend shifts with the cook. The third element, churma, is a dish in its own right, a sweet made by crushing fried or baked wheat with ghee and sugar, and it deserves its own article rather than being crowded in here. Treated honestly, dal baati is a study in how a deliberately hard bread becomes the center of a meal once it meets enough dal and ghee.