Preheat the oven to 350 degrees F. Grease 2 9-inch round cake pans.
Mix yellow cake mix, sour cream, vegetable oil, water, sugar, flour, eggs, 1/2 teaspoon vanilla, 1/2 teaspoon butter extract and salt together in the bowl of a standing mixer with a paddle attachment. Beat on low speed for 2 minutes. Divide batter between the prepared pans and bake for 30 to 35 minutes. Cool in the pan a few minutes, and then transfer to a wire rack to cool completely.
Place 1 cooled cake onto a cake platter. Ice just the top half with the Crusting Buttercream Icing. Place the second cake on top. Lightly ice the sides and top of cake. Gently place your hands on top of the iced cake and press down softly. Doing this helps to mold the cake to the pressure of when the fondant goes onto the cake. It will deter the cake from getting a visible ring that will show through when fondant covers the cake.
After the fondant has sat in the fridge it will be hard. When ready to use, place in the microwave for a few seconds, maybe 10 seconds at a time, as to soften but not melt. Once it's a little softer it will be ready to work with. Start kneading away on a powdered sugar covered surface just to wake it up a little.
Flour the surface and the rolling pin with powdered sugar. Roll the fondant to a thickness of about 1/4-inch. Roll the fondant around the rolling pin to transfer it to the top of the cake. Use your fingers to position the fondant gently on top of the cake, smooth out the top and sides. Cut away the excess with a knife, using the bottom of the cake as the guide. With the extra fondant, cut out designs either by hand or using a cookie cutter. Place the designs onto the cake. Use a dab of water to act as the glue to adhere the designs to cake.
Crusting Buttercream Icing:
Cream the shortening in the bowl of a standing mixer with a paddle attachment. Add 1/2 teaspoon vanilla and butter flavorings each. Add the powdered coffee creamer to the water and stir. Once the coffee creamer is dissolved, add this mixture to the shortening and mix on low until the water is incorporated into the shortening. Slowly add the powdered sugar into the shortening, mixing on low speed.
Cook's Note: Once the powdered sugar is added, you may need to add a little more water depending on what consistency you want your icing.
Combine the powdered sugar and a dash salt and spread out on the counter to make a 12-inch circle.
Coat the inside of a large microwave-safe bowl with shortening. Place the marshmallows, 1/2 teaspoon of each flavorings, and water and/or colorings in the bowl. Microwave on high for 1 minute (the marshmallows should be puffy). Stir the mixture with a rubber spatula and place back in the microwave for 30 second intervals, or until the marshmallows are melted and smooth when stirred. (While this mixture is in the microwave, coat your hands with shortening as the fondant is sticky and messy.)
Once the marshmallows are melted and smooth, transfer the contents of the bowl onto the powdered sugar. Start working the sugar into the melted mixture, kneading it like you would bread dough. Continue kneading until the mixture loses its stickiness; you may have to add more powdered sugar. You'll know when it's ready if the fondant forms into a ball. Coat the fondant ball well with shortening and wrap in plastic wrap. Place the fondant in refrigerator for at least 6 to 8 hours or overnight.