(At least one day before serving, preheat the oven to 300°F.) Adjust a rack to the middle position and preheat the oven to 300°F.

• In a small heavy saucepan, combine the sugar and 1/4 cup water and stir until the sugar is completely moistened. Bring to a boil over medium-high heat, stirring occasionally, until the mixture turns brown. Continue to simmer, gently turning the pan, until the sugar has turned a honey color. Remove the pan from the heat and swirl it for 15 to 20 seconds, or until the sugar is reddish-amber and aromatic. 2 tablespoons warm tap water, carefully swirled in until combined – be careful as the mixture may bubble and steam. The entire procedure should take no more than 10 minutes.
• Remove the caramel from the skillet and pour it into an 8-1/2 x 4-1/2-inch loaf pan. (Note: When you pour the caramel into the loaf pan, it will solidify; this is OK; it will soften as it bakes.) Set the loaf pan aside. (Fill the saucepan halfway with water and bring it to a boil to remove the solidified caramel.)
• In a large mixing basin, whisk together the eggs and yolks until well blended. Whisk together the sweetened condensed milk, evaporated milk, full milk, vanilla, Bourbon, and salt until well combined. To eliminate any fragments of egg, strain the mixture through a fine-mesh strainer into a large mixing basin; then pour the strained custard into the loaf pan over the caramel. Cover the loaf pan completely with aluminum foil
• To prepare a water bath, place the loaf pan in the center of a 9×13-inch baking or roasting pan (ideally with high edges). Place the nested pans in the oven, then pour hot water around the loaf pan with a tea kettle or pitcher until it reaches halfway up the sides. Bake for 75 to 90 minutes, or until the custard is firm around the edges but still jiggly in the middle. (Don’t worry if the custard appears undercooked; it will continue to cook as it cools, and the center will set completely — I swear!) Remove the pans from the oven carefully. Remove the foil and cool the flan for 1 hour in the water bath.
• After removing the loaf pan from the water bath, wipe it dry. Refrigerate overnight or for up to 4 days, carefully wrapped in plastic wrap.
• Carefully glide a sharp knife over the pan’s edges to unmold the flan. Turn the pan and platter over, inverting a dish with a raised rim on top of the flan to contain the liquid caramel. If the flan does not release right away, invert it for a minute and it should glide right out. If it still won’t come out, go around the edges with the knife again. Remove the loaf pan after the flan has been released. Scrape the remaining caramel onto the dish with a rubber spatula. It’s fine if you don’t manage to release all of the caramel. Cut the flan into separate portions and ladle the sauce over them. (Leftover flan can be wrapped loosely in plastic wrap and stored in the refrigerator for up to 4 days.)

Note: If you don’t want to use the Bourbon, use an extra 2 teaspoons vanilla extract instead.