How to Thicken Ganache
To thicken your ganache, try putting it in the fridge for an hour. After half an hour, take it out and stir it to help it set. If you don't have an hour to wait, try adding more melted chocolate. For a thick ganache, you'll want twice as much chocolate as cream. For a frosting ganache, use equal amounts of chocolate and cream. Alternatively, chill and beat your thin ganache to make whipped ganache. Just put it in the fridge for an hour. Then, use a hand mixer to beat the ganache until it turns fluffy. You can use whipped ganache to frost a cake or as a dip for fresh fruit and cookies.
Use a higher chocolate-to-cream ratio to produce a thicker ganache. Milk chocolate, white chocolate, and compound chocolate all melt down to a thinner consistency than dark chocolate does. For a thicker ganache, like for truffles, use a 2:1 ratio of chocolate to cream. For a frosting ganache, use a 1:1 ratio. For a thin, pourable ganache, use a 1:1.5 ratio. Compound chocolate is made of cocoa, sweeteners, and vegetable fat, and it melts down a little differently than baking chocolate does. Because of this, you do need a higher ratio of chocolate to cream than you would with couverture chocolate. When you measure out the chocolate and cream, use a scale rather than measuring cups to be as precise as possible. Add more chocolate to your ganache if you live somewhere warm. Higher temperatures will affect the viscosity of your ganache. If it's warm enough that the chocolate softens or starts melting when it's on the counter, plan on adding an additional 2 to 3 ounces (57 to 85 g) of chocolate to your recipe. Especially for recipes where you need a sturdier ganache, like for truffles or for frosting between layers, you want to err on the side of too-thick rather than too-thin ganache. Chill and beat too-thin ganache to turn it into whipped ganache. Cover the ganache with plastic wrap and set it in the fridge for an hour. Take it out and use a hand-mixer to beat the ganache until it gets fluffy and turns a lighter shade of brown. Use the whipped ganache to frost between layers of a cake or to decorate the top of baked goods. Use whipped ganache as a dip for fresh fruits or cookies. Put ganache into the fridge to let it set and get thicker. Hot or warm ganache will always be thinner than ganache that has chilled for an hour. If you have the time, take your ganache, cover it with plastic wrap, and set it in the fridge. Leave it in the fridge for an hour, taking it out every 30 minutes to stir it. Once it gets to the right consistency, proceed with your recipe. It's possible that the ganache won't thicken, no matter how long you leave it in the fridge. If that's the case, you'll need to reheat it and add more chocolate to give it a thicker consistency. Reheat the ganache on the stovetop or in the microwave. If the ganache still isn't thick enough after you've chilled it, then it's time to try reheating it and adding more chocolate. If you're using the stovetop, transfer the ganache to a saucepan and put it over low heat, stirring continuously. If you're using the microwave, put the ganache in a microwave-safe bowl and heat it in 15 second increments, stirring it between each session, until the ganache is warm and runny again. Stirring the ganache frequently will keep it from burning. Use low heat or small increments of heat to safely warm up chilled ganache. Incorporate 1 ounce (28 g) of chocolate at a time to the warmed ganache. Weigh and add chocolate in increments. After each ounce, stir the ganache until the new addition is completely melted. If you're using the microwave, add the chocolate to the bowl and stir the ganache before microwaving it again—the heat from the warm ganache may be enough to melt the new chocolate on its own. If it's needed, put the bowl back into the microwave for 10 to 15 seconds. If, somehow, the ganache becomes too thick, add 1 ounce (28 g) of cream to the mixture. Stir the ganache and add chocolate until the consistency is right. Until the ganache reaches the right thickness, keep adding 1 ounce (28 g) of chocolate at a time. If you're using the microwave, use your best judgement to know when to microwave the ganache again. If you're using the stovetop, keep the heat as low as it'll go to prevent the bottom from burning. With the microwave, the danger is that you'll accidentally cook the ganache for too long, making it dry and hard. Remove the ganache from the heat and let it cool, or use it right away. Once you think you've achieved the right consistency of ganache, remove the pot or bowl from the heat. Let it cool down on the countertop for an hour, or use it right away. Luckily, the ganache should taste great, no matter the consistency! 
Use a higher chocolate-to-cream ratio to produce a thicker ganache. Add more chocolate to your ganache if you live somewhere warm. Chill and beat too-thin ganache to turn it into whipped ganache. Put ganache into the fridge to let it set and get thicker. Reheat the ganache on the stovetop or in the microwave. Incorporate 1 ounce (28 g) of chocolate at a time to the warmed ganache. Stir the ganache and add chocolate until the consistency is right. Remove the ganache from the heat and let it cool, or use it right away. 