I have been practicing making a topsy turvy cake for my cousin's wedding. I have been following the instructions in Sharon Zambito's DVD. I made the chocolate ganache to put under the fondant but it didn't get super hard like hers did in the DVD. I'm wondering if the quality of chocolates used makes a difference?? Or did I get the ratios wrong? I used 2 cups of choc chips and 1 cup of heavy whipping cream. Please help. I want this cake to be perfect.

Chill the ganache until the outside edge has completely hardened but the middle is still soft. Then mix that (with a food processor if available) and the whole mass will set properly.

It's not you or the recipe--it's the chocolate. Some brands need to be chilled this way to start the "set".

You shouldn't be making ganache using volume measurements, only by weight so whatever one cup of cream weighs, you need to weigh out the same amount of chocolate. Also, chocolate chips that aren't courveture contain something in them to make them bakestable. Try using either courverture chocolate or at least 70% cocoa solid chocolate bars - oh and always weigh your ingredients (also make sure you are using heavy whipping cream).

I don't have a kitchen scale. Is there a recipe I can use. I bought two good quality chocolate bars today that are 225 g each. So how much cream would I use? If I remember from high school science, aren't grams and milliliters the same? So 450g of chocolate and 225 ml of heavy cream???

The ratio is good! What is the brand of your chocolate? Does Sharon say to leave it at room temperature for a few hours before using? That's when you get the true consistency of your ganache. It usually gets hard when you put it in the fridge.