3 ½ cups sugar, divided
10 egg whites
1 pinch salt
Zest of 1 lime

Pour 2 cups sugar into a 10-inch bundt pan. Cook over medium heat, directly on the stove top burner, until the sugar melts completely and turns golden brown, 10 to 12 minutes. Swirl the pan allowing the caramel to completely cover the base and about 1-inch up the sides of pan. Set aside to cool and harden.
Preheat oven to 350°F.
In a bowl of a standing mixer with the whisker attachment, combine egg whites and salt. Beat on medium-high speed until stiff moist peaks form, about 5 minutes. Turn speed to medium and slowly pour remaining 1 ½ cup sugar; beat until well incorporated, 2 minutes. Turn off mixer and fold in lime zest.
Scoop meringue into bundt pan and cover tightly with aluminium foil. Place bundt pan into a large ovenproof baking pan filled up with warm water up to half way. Carefully transfer to oven. Bake for 40 minutes, or until a knife inserted in centre comes off clean.
Remove foil and allow cooling to room temperature. Unmold flan by carefully flipping it over a large plate. Refrigerate for at least 3 hours before serving.