Heat 1 cup sugar and ¼ cup water in a saucepan over medium heat without stirring until amber color appears, about 6-8 minutes. Pour immediately into ramekins or flan mold, swirl to coat the bottom evenly, and let cool 5 minutes to harden.
1 cup granulated sugar, 0.25 cup water
Heat whole milk in a saucepan over medium heat until steaming but not boiling, about 5 minutes. Remove from heat, stir in vanilla extract and salt, and let cool 3 minutes to prevent scrambling eggs.
3 cups whole milk, 1 pinch salt, 2 tsp vanilla extract
Whisk eggs and ⅓ cup sugar in a large bowl until blended but not frothy. Slowly pour warm milk into eggs in a steady stream while whisking constantly for 1-2 minutes to avoid curdling. Strain custard through a fine mesh strainer into a clean bowl.
6 large eggs, 0.33 cup granulated sugar, 3 cups whole milk
Pour custard into caramel-coated ramekins. Place ramekins in a baking dish, fill dish with hot water halfway up sides of ramekins, and bake at 325°F for 45-55 minutes until edges are set firmly but center jiggles slightly when shaken.
Remove ramekins from water bath carefully and cool on a wire rack for 30 minutes. Cover with plastic wrap and refrigerate at least 4 hours or overnight until custard firms completely and caramel becomes liquid.
