½ cup whole milk (half-and-half or 2% milk may be substituted but do not use skim milk)
2 teaspoonsvanilla extract
1 tablespoonBourbon (see note)
(This recipe should be made at least one day before serving.) Adjust a rack to the middle position and preheat the oven to 300°F.
Stir together the sugar and 1/4 cup water in a medium heavy saucepan until the sugar is completely moistened. Bring to boil over medium-high heat and cook, without stirring, until the mixture begins to turn golden. Gently swirling the pan, continue to cook until sugar is a honey color. Remove from the heat and swirl the pan until the sugar is reddish-amber and fragrant, 15 to 20 seconds. Carefully swirl in 2 tablespoons of warm tap water until incorporated – be careful as the mixture will bubble and steam. This whole process should take less than 10 minutes.
Pour the caramel into an 8½ x 4½-inch loaf pan; do not scrape out the saucepan. Set the loaf pan aside. (To clean the hardened caramel from the saucepan, fill the pan with water and bring it to a boil.)
Whisk the eggs and yolks in large bowl until combined. Add the sweetened condensed milk, evaporated milk, whole milk, vanilla, Bourbon, and salt and whisk until incorporated. Strain the mixture through a fine-mesh strainer into a large bowl to remove any bits of egg; then pour the strained custard into the loaf pan over the caramel.
Place the loaf pan in the center of a 9×13-inch baking or roasting pan (preferably with high sides) to make a water bath. Place the nested pans in the oven; then, using a tea kettle or pitcher, pour hot water around the loaf pan until it reaches about halfway up the sides of the loaf pan. Bake for 75 – 90 minutes, until the custard is set around the edges but still a bit jiggly in the center. (Don’t worry that it seems undercooked. The custard will continue to cook as it cools, and the center will set completely — I promise!) Carefully remove the pans from the oven and leave the flan in the water bath for 1 hour to cool.
Remove the loaf pan from the water bath and wipe the pan dry. Cover tightly with plastic wrap and chill in the fridge overnight or up to 4 days.
To unmold the flan, carefully slide a sharp knife around the edges of the pan. Invert a platter with a raised rim (to contain the liquid caramel) on top of the flan and turn the pan and platter over. If the flan doesn’t release immediately, let it sit inverted for a minute and it should slide out. When the flan is released, remove the loaf pan. Using rubber spatula, scrape the residual caramel onto the platter. You won’t be able to release all of the caramel – that’s okay. Slice the flan and spoon the sauce over individual portions. (Leftover flan may be covered loosely with plastic wrap and refrigerated.)
Note: If you would like to omit the Bourbon, replace with an additional 2 teaspoons of vanilla extract.