This year Adventure Boy wanted a geode ice cream cake for his birthday. I was up to the challenge of a geode cake but there was one small problem. Geode cakes are made with rock candy. I don’t live near a store that would sell rock candy and I didn’t have the days required to grow the crystals. Yes, you can make a geode cake without rock candy. The answer is homemade candy. Here is my tutorial on assembling a geode ice cream cake.

Homemade hard candy may be easier to make than you think. It is just a matter of boiling a sugar mixture on the stove. The key to success is using a quality candy thermometer and watching it closely. In this recipe the sugar mixture is heated to 300℉ which is hard crack stage. Most candy thermometers have “hard crack” stage marked on them to help candy makers. Make sure that your sugar mixture reaches 300℉ but immediately remove it from the heat so it does not burn or get hotter than 300℉. Temperature in candy making is an exact science in this way.

Equipment Needed to Make Amethyst Rock Candy

A candy thermometer
A medium saucepan, preferably with a thick bottom
A 9” x 13” or a 11” x 13” baking dish lined with foil

Ingredients for Amethyst Rock Candy

1/2 cup water
3/4 cup light corn syrup. If you are wanting to avoid GMOs be sure to buy organic. I used Wholesome brand, which is organic.
2 cups sugar
2 teaspoons vanilla extract
24 drops red food coloring, not gel. I used McCormick.
16 drops blue food coloring, not gel.

How to Make Amethyst Hard Rock Candy

Prepare a glass baking dish by lining it with aluminum foil. Both an 11 x 7” or a 13 x 9” baking dish will work. Lightly grease the foil.

In a pot add the water, light corn syrup, sugar, and vanilla. Stir to combine. You can substitute any flavoring extract for the vanilla at the same ratio. The vanilla is a mild flavor that matches the purple color and generally goes well with all cake flavors.

Add the food coloring. The amethyst color at this point is a deep purple. It will become lighter when it hardens and cools. Heat over medium heat while stirring constantly.

When your mixture begins to boil, stop stirring. Stirring after this point will interrupt the cooking process of the sugar. Insert a candy thermometer. Be sure that the point of thermometer is under the surface level of the liquid but not touching the bottom of the pan.

When your mixture reaches hard crack stage at 300℉, remove it from the heat. This will take 10-15 minutes or so. Be sure that the mixture fully reaches 300℉ but do not allow the temperature to rise higher than that. Watch your thermometer carefully. When the bubbling has died down, pour the mixture into your prepared baking dish. Any bubbles present at this stage will disappear.

Allow the mixture to cool completely, about 45 minutes to one hour. Remove the candy from the baking dish by removing the foil from the baking dish sides and then turning the baking dish upside down. Hit your hard candy with a large mallet until it breaks into large chunks. Place one large chunk into a Ziploc bag and hit with a mallet until the desired size of crystals is achieved.