Place 2 tablespoons butter and chopped chocolate in a microwave safe bowl and microwave according to directions on chocolate package. This can also be done in a double boiler; heat small amount of water on stove top but do not allow it to boil. Place another heat safe bowl tightly over the top and turn off stovetop once water is warm. Be careful to not allow any water moisture to get in chocolate/butter mixture. Water will curdle/burn chocolate. Stir until melted. Meanwhile, in a small saucepan, combine heavy cream and lemon zest. Allow zest color to combine with cream and heat on low for a few minutes, careful not to boil mixture. Add corn syrup and lemon extract to mixture and stir. Immediately combine chocolate and cream mixture and stir for a few minutes until the mixture becomes silky smooth from the heat. Cover and refrigerate for about 2 hours. Remove from the refrigerator and scoop out teaspoon size balls of chocolate. Roll between hands to get even texture then roll in yellow or white sanding sugar until coated completely. Store in refrigerator until ready to serve.