Preheat Oven: Preheat your oven to 180°C (350°F). Grease a clay baking dish thoroughly with butter.
Mix Eggs and Sugar: In a bowl, whisk eggs and sugar together until smooth.
Add Milk and Flavorings: Gradually whisk in milk, flour, vanilla extract, lemon zest, and a pinch of salt. Ensure mixture is lump-free.
Pour Custard into Clay Dish: Pour the mixture into the greased clay dish. Tap gently on the counter to remove air bubbles.
Bake Slowly: Place the dish in the oven and bake for 35–45 minutes. The custard should be golden on top and slightly firm when jiggled.
Cool: Let it cool for at least 20 minutes before serving. The custard will firm up slightly as it cools.
Serve: Slice into wedges or scoop into bowls. Optionally, sprinkle with cinnamon or powdered sugar.