Buttercream frosting help!!!
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Do you mean it's hard as a rock or that it has a light crust on the outside? If you are using a recipe with fat (either butter or shortening or a combination) and powdered sugar, it's probably crusting which is normal. To not get it to crust, you need to either increase the fat, decrease the powdered sugar, or add more liquid.
If it's totally hard then you need to look at another recipe, or add more fat and liquid to your existing one.
What Annie said plus my 2 cents.....
If the crust is not what you want make one of the "mbc" icings.
Both types rely on cooked sugar and meringue and butter.
The texture and mouthfeel is smooth and silky...not gritty at all.
Google search Italian or Swiss buttercream for a recipe.
I see that you are attending a culinary academy.
My suggestion is either ask the pastry instructor or one of your peers to point out the chapter in the textbook.