In many candy recipes, butter and margarine can be used interchangeably. It is best to use butter when the flavor of the butter contributes to the taste of the candy, such as in toffee, and margarine when the taste is predominately another flavor, such as in peanut butter or chocolate.
Candy made with milk products will cook with a residue on the bottom of the saucepan, so the candy must be stirred while cooking to prevent sticking and scorching. Heavy cream or nondairy coffee creamers are often used in recipes instead of milk for a richer flavor. These products will not stick and do not need to be stirred. Heavy cream or nondairy products yield a better quality candy, and there is very little chance of the candy becoming granular.
Candies with a sugar, corn syrup and water base should be stirred well to mix the sugar completely with the liquid, covered with a lid and brought to a rolling boil. Remove the lid, insert the candy thermometer and cook the candy to the desired temperature without stirring. Covering the candy the first few minutes of cooking prevents sugar crystals from forming on the side of the pan and eliminates the possibility of grainy candy. Use of a lid eliminates the need of washing down the side of the saucepan with a wet pastry brush. Never use a lid when preparing recipes calling for milk or cream or mixtures that might boil over.