Melt the cocoa butter over a double boiler until it reaches 90°F.
Place the confectioners' sugar, fondant and corn syrup or glucose in the bowl of a mixer fitted with the paddle attachment. Add the melted cocoa butter and mix on low speed until well combined, approximately 5 to 7 minutes.
If the cocoa butter separates from the mixture during mixing, let it cool for 15 to 30 minutes and then mix again. Wrap the modeling chocolate in plastic wrap and store in the refrigerator before using.
* FYI: The cocoa butter brand that I use is by LorAnn Oils. It can be found in some cake decorating supplies stores or online.