Cut and arrange all dippers for fondue (fruit, cookies, cake, etc.).
Fill bottom of a double boiler pot with water and place over high heat until water is boiling. If a double boiler pot is not available, use a heat-safe bowl over a pot of boiling water.
Reduce to medium heat and add heavy cream to the top layer of double boiler (separate from the water). Once cream comes to a simmer, add chocolate 2 ounces at a time, whisking with a silicone whisk until smooth.
Continue adding chocolate until all chocolate is melted. Whisk in vanilla extract.
To serve, pour chocolate into fondue pot, lighting flame underneath to keep warm (or if electric, turn on low heat). Stir occasionally, taking care not to burn chocolate.