Heat oven to 350ºF.
In the saucepan, combine the milk, half-and-half, vanilla, and sugar. Bring to a bare simmer over medium-low heat.
Next, place 1 to 2 tablespoons of each topping into each of the custard cups. The topping should come a few millimeters up the side of the custard cup.
Separate 3 of the eggs using a slotted spoon. Reserve the whites for another use. (Note: Freeze the whites in ice trays. After the whites are frozen, place the frozen cubes into zip-top freezer bags. The frozen whites can be frozen up to a year.)
Place a mixing bowl on a rubber pad or a wet towel to prevent the bowl from spinning out of control. In the mixing bowl, combine the 3 remaining whole eggs and the 3 yolks. Whip the eggs with a whisk until slightly thickened and lightened in color. While whisking the eggs, drizzle in about a quarter of the hot milk. Now whisk the tempered eggs back into the saucepan with the remaining milk mixture.
Place a fine-mesh strainer over a glass or stainless steel bowl with a spout. Pour the egg mixture through the strainer in order to catch any curdled egg bits or particles that may be in the mixture.
Place the custard cups into the roasting pan. Evenly distribute the custard into the cups, going short on the first pass. Place the pan on the middle rack of the oven and pour boiling water into the pan just under the level of the custard.
Cook the flans until they wobble slightly when the pan is wiggled, about 40 minutes. You can also insert a paring knife midway between the edge and the center. If it comes out clean, the flans are done. Using tongs, remove the cups from the pan to a towel-lined sheet pan. Allow the water in the roasting pan to cool before discarding. Cool, cover, and chill until ready to serve.