Heat the oven to 325°F (165°C). Set a dry 6-cup solid metal ring mold or 8-by-4-inch metal loaf pan beside the stove. Heat the sugar and water in a small saucepan over medium heat. Once boiling, swirl occasionally without stirring until amber, about 8–12 minutes.

Carefully pour the hot caramel into the pan. Using oven mitts, tilt the pan to coat the base. Let it harden while you prepare the custard. Hot caramel can burn severely, so keep hands clear.

Whisk condensed milk, whole milk and eggs gently until smooth. Strain into the caramel-lined pan and cover loosely with foil. Place it in a roasting pan on the oven rack. Pour hot water into the outer pan to reach halfway up the mold.

Bake 55–80 minutes depending on the mold, until the edges hold, the center trembles as one piece and reaches at least 160°F. Remove from the bath, cool on a rack for 30 minutes, then refrigerate covered for at least 4 hours.

Run a thin knife around the edge. Dip the base briefly in warm water, place a rimmed platter over the pan and invert in one movement. Let caramel run over the custard before slicing.