Actually, Cake decorating is not one of my fortes. I do know that you can also make roses from Gum Paste. There is kosher gum paste on the market which can be made in many colors. There are many great books on the market which will help you in decorating and frosting cakes. If you need a reference where to get any cake necessities and unique ingredients, let me know. I can advise you on that. As for butter cream, I try to stay away from it. I prefer whipped cream, either dairy or pareve.
Here is a very good sauce recipe:
10 to 12 fresh plum tomatoes (approximately 2 to 2 1/2 pounds)
4 ounces extra-virgin olive oil, plus additional extra-virgin olive oil, optional
3 cloves garlic, finely chopped
Pinch crushed red pepper
1/2 medium onion, finely chopped
Kosher salt
Freshly chopped parsley leaves
Peel tomatoes by scoring the skin of each tomato with a sharp knife (do not cut too deep). Then, place scored tomatoes into a pot of boiling water and boil for approximately 1 to 1 1/2 minutes. Remove tomatoes and plunge into cold water. Peel and dice tomatoes and set aside.
Heat olive oil in a saucepan. When hot, add garlic and crushed red pepper. Saute until garlic turns slightly golden. Add chopped onion and saute an additional 2 1/2 minutes.
Add chopped plum tomatoes and cook approximately 5 minutes. Add salt to taste. Add chopped parsley and extra virgin olive oil if desired, just before using.
Enjoy and let me know how it comes out.