Step 1In a medium saucepan, combine the milk, the cream and two-thirds cup of the sugar. Bruise the sprigs of rosemary or thyme with a mallet to lightly crush them. Add the herbs to the milk mixture in the saucepan, and bring to a simmer over medium heat. Remove from the heat, cover and let the infused milk steep for 1 hour. Strain the mixture through a cheesecloth-lined strainer. Lift the cheesecloth out of the strainer, and squeeze out any remaining liquid from the herbs, then discard them.
Step 2Heat the oven to 350 degrees. Place the remaining two-thirds cup sugar into a heavy-bottomed skillet and heat over medium heat. Shake the pan so that the sugar is evenly distributed in the bottom of the pan. Tilt and move the pan around on the burner to prevent hot spots, and heat until the sugar caramelizes to an amber color, 5 to 6 minutes.
Step 3Pour the caramelized sugar evenly into the bottom of a 2-quart, round, glass baking dish. If necessary, tilt the baking dish back and forth so the bottom is evenly coated with the caramel. Allow the caramel to cool.
Step 4Whisk together the egg yolks and eggs just until blended. Whisk the infused milk mixture into the eggs and strain.
Step 5Put the caramel-lined baking dish into a deep, 13-by-9-inch pan and pour the egg custard mixture into the baking dish. Pour in enough hot water to come halfway up the sides of the pan to the level of the custard. Carefully put it in the oven.
Step 6Bake until the flan is set and the center has a slight jiggle, about 1 hour to 1 hour, 10 minutes. Remove from the oven and let cool, then cover and chill overnight.
Step 7When you're ready to serve, loosen the sides of the flan with the tip of a knife or a small spatula and invert the flan onto a large serving plate. If you have a problem removing the flan, dip the baking dish into a pan of hot water to loosen the bottom and sides.