Chocolate ganache is a basic cake filling that is a combination of heavy cream and chocolate. Cream cheese filling is made by combining cream cheese with butter and powdered sugar. Basic buttercream filling contains powdered sugar, milk, butter and vanilla.
Make a variety of fillings by starting with basic buttercream filling. Place 1 pound of powdered sugar into the bowl of an electric mixer, add 1/2 cup of milk, 1/2 teaspoon of vanilla and 1/8 teaspoon of salt. Beat at low speed until smooth. Cut 2 sticks of butter into 1/2-inch slices, adding them one at a time while the mixer is running. Once the butter is thoroughly incorporated, add 1/2 cup of vegetable shortening, beating for 12 minutes on the mixer's highest speed. To make chocolate chip filling, add 1 cup of crushed chocolate chips. Add banana instant pudding mix with the powdered sugar for banana cream filling.
To make lemon curd filling, combine in a large bowl 5 whole eggs and 5 egg yolks in addition to 1 1/4 cups of lemon juice, 1 2/3 cups of granulated sugar, 1 1/2 tablespoons of lemon zest and 3/4 cup plus 1 teaspoon of melted butter. Whisk the ingredients until smooth, place the bowl over a pot of boiling water, stirring frequently until the mixture thickens. Cover it with plastic wrap, and chill.
To make chocolate mousse filling, combine in a microwaveable bowl 3/4 cup of dark chocolate and 4 tablespoons of butter. Microwave for 40 seconds until the butter and chocolate are melted. Stir in 1/2 teaspoon of dark rum and 1/2 cup of heavy cream, mixing it until smooth. In a large bowl, combine the chocolate mixture with 1 1/2 cups of heavy cream, whipping by hand or with a mixer until it forms stiff peaks. Cover it with plastic wrap, and chill.