Kitchens (like bakery, tailor or manufactures) are a more specialized analog of workshops.

To give orders to a kitchen, go to Crafting > Cooking tab, which appears once you've discovered cooking: {{villagetab:village:kitchen_orders.png}}

Kitchens are significantly (2.5 times!) more efficient in cooking food compared to workshops, so it makes sense to handle all your cooking here, barring the emergencies.