1 C butter, room temp (must be BUTTER)
1 C Crisco
2 t vanilla extract
5 T heavy cream
2 lbs powdered sugar
Cream together butter and Crisco until smooth. Beater to low and add extracts. After extracts are incorporated, add cream. After all are mixed in, slowly add in powdered sugar until all incorporated. For stiff consistency, start with 3 or 4 T cream, depending on humidity. Less is easier to add to. It's harder to thicken than it is to thin out. Gradually add until you reach desired consistency. You can also add 1 T or more of corn syrup as needed to thin out. This also gives a little elasticity if you are planning on doing a lot of strings or writing.
I like to do 1 t vanilla and 1 almond extract. You can play around with flavors if you like. You can also adjust your fats. Crisco holds up a lot better in heat or if you tend to be hot handed when you decorate. You can also add 2 T meringue powder to stabalize your icing and prevent colors from bleeding. This recipe is crusting without the meringue powder, however.