Preheat your oven to 450°F. Grease the ramekins with butter. Wash and dry the lime. Zest the lime and heat the zest with the milk in a saucepan.

Separate the egg yolks from the whites. Whisk the yolks with the sugar. Add the flour and cornstarch, and mix well. Gradually pour in the hot milk while whisking constantly. Pour the mixture back into the saucepan and cook over low heat, stirring, for about 5 minutes until thickened. Remove from heat and let cool slightly.

Beat the egg whites until stiff peaks form, then gently fold them into the mixture with a spatula. Fill the ramekins two-thirds full and bake immediately for 10 minutes. Then lower the oven temperature to 300°F and continue baking for 15 to 20 minutes. Do not open the oven door! Serve immediately after removing from the oven.