Fondant should not be made until you you are ready to use it; be sure the simple syrup is cooled and petits fours are cut before making the fondant.
Set a heatproof bowl, or the top of a double boiler, over a pan with 2 inches of simmering water. In a small saucepan, heat 1/4 cup water to 110 degrees. Place half the powdered fondant, the water, salt, corn syrup, and butter in the bowl of simmering water. Using a spatula or a wooden spoon, stir the ingredients together until smooth, about 3 minutes. Work quickly; the fondant will lose its sheen if it is heated over 95 degrees or for a prolonged period of time. Add the remaining powered fondant and flavoring, and stir until smooth. The fondant should look glossy, and its density should be slightly thicker than pancake batter. If desired, use a toothpick to add the food coloring a bit at a time; stir with spatula or wooden spoon until combined. If you are using more than one batch of fondant, make and use them separately.
If the fondant is too thick to pour, add simple syrup, 1 teaspoon at a time, to thin, as necessary.