Wash and dry the Silicone Chocolate and Candy Molds.
Get a 4-quart saucepan. Over low heat, melt the cubed butter, stirring occasionally until it is nearly melted. Add the sugar, sour cream, and salt. Raise the heat to medium and stir until the sugar melts.
Continue to stir the mixture until it boils. Get a candy thermometer and cook until it reaches 235 degrees F (113 degrees C), while stirring continuously.
When the temperature reaches 235 degrees F (113 degrees C), remove from heat and add the marshmallow cream and white chocolate chips. Stir until well melted. You may return to the heat for a few seconds to help melt it.
When the fudge mixture is melted, add the lemon oil or extract, lemon zest, citric acid, and a few drops of food coloring if preferred. Stir until well combined. Taste and add more citric acid or food coloring as desired.
Once you reach the desired color and taste, pour the mixture into the Silicone Chocolate and Candy Molds. Let it set at room temperature for 3 to 4 hours, or let it cool in the fridge for about an hour or two.
When they are hardened, pop them out of the molds, wrap them in colored candy paper or store in airtight containers.