This is a recipe from the Wilton Cake Decorating yearbook. It is a lot more work than buttercreme but it sure makes an elegant cake. Wilton does make a ready to use Rolled Fondant, you may want to check this out if you don't want to go through the trouble of making it.

Rolled Fondant

This icing is rolled out and used as a covering for a pound or fruit cake, which is traditionally first covered with a layer of marzipan to seal in flavor and moistness of the cake. A light layer of buttercream may also be used. Cakes covered with rolled fondant can be decorated with royal or buttercream icing.

1 Tbsp. unflavored gelatin
1/4 cup cold water
1/2 cup glucose
1 Tbsp. glycerin
2 Tbsp. solid vegetable shortening
2 lbs. confectioners sugar
2-3 drops liquid food color and flavoring, as desired.

Combine gelatin and cold water; let stand until thick. Place gelatin mixture in top of double boiler and heat until dissolved. Add glucose and glycerine, mix well. Stir in shortening and just before completely melted, remove from heat, add flavoring and color. Mixture should cool until lukewarm. Next place 1lb. confectioners sugar in a bowl and make a well. Pour the lukewarm gelatin mixture into the well and stir with a wooden spoon, mixing in sugar and adding more, a little at a time, until stickiness disappears. Knead in remaining sugar. Knead until the fondant is smooth, pliable and does not stick to your hands. If fondant is too soft, add more sugar; if too stiff, add water a drop at a time.
Use fondant immediately or store in airtight container in refrigerator. When ready to use bring to room temperature andknead again until soft.

Spray work surface and rolling pin with vegetable oil pan spray and dust with a mixture of confectioners sugar and cornstarch. Roll out fondant into a circle the diameter of the cake plus double the height of the cake you are covering. As you roll, lift and move the fondant to prevent it from sticking to the surface. Gently lift fondant over rolling pin and place over cake. Smooth and shape fondant on cake using palm of hand. If large air buubbles are trapped under fondant prick with a pin and continue to smooth. Trim excess from base.