In a medium pan, bring sugar, water, corn syrup and lemon juice to a simmer, without stirring, over medium-high heat. Wipe any sugar crystals off the sides of the pan with a wet pastry brush because they can cause the syrup to be grainy. Continue to cook until the syrup turns from clear to golden, swirling the pan continuously for even browning until large, slow bubbles on the surface turn honey-caramel in color.
Remove the pan immediately from the heat, and working quickly (and carefully - it's very hot!), pour a portion of the caramel into each of 8 ungreased 6-ounce ramekins. Allow the caramel to cool and harden, about 15 minutes.
Preheat oven to 350 degrees (make sure rack is in the middle).
Heat milk and cream in a medium saucepan over medium heat, stirring occasionally, until steam appears - usually 6-8 minutes- remove from heat.
Meanwhile, gently whisk the eggs, yolks, and sugar in a large bowl until just combined.
Off the heat, gently whisk the warm milk mixture into the egg mixture, adding vanilla and salt.
Strain the mixture through a fine mesh cloth into a large measuring cup or a bowl with a pouring spout. Set aside.
Place the ramekins in a large baking dish or roasting pan and divide and pour the custard mixture evenly into them.
Fill the pan with about two cups of boiling water so that it reaches about half way up the sides of the ramekins. At this point you can cover the pans loosely with aluminum foil, allowing the steam to escape.
Bake until a paring knife inserted halfway between the center and edge of the custards comes out clean, about 35 to 40 minutes.
Transfer to a wire rack and allow to cool to room temperature.
To unmold, slide a paring knife around the perimeter of each ramekin. Holding a serving plate over the top of the ramekin, invert and set on the work surface. Gently shake the ramekin to release the custard.
The room-temp, finished, baked flan can be chilled in the fridge (loosely covered with plastic wrap) for up to 2 days.