Spray two muffin tins with nonstick spray. (If you only have one pan, work in two batches: 12 Ritz crackers, 1/2 cup butter, and 1/2 cup brown sugar at a time.)
Add a Ritz cracker to each muffin tin cup.
Add the butter and brown sugar to a saucepan and heat until boiling. Boil 2-3 minutes, until the temperature reaches 300 degrees Fahrenheit.
Carefully add about 1 tablespoon of the toffee mixture over each Ritz cracker. If you have extra, divide it among the cups.
Bake in the oven for 4 minutes.
Remove from the oven and sprinkle the chopped chocolate over the top.
Allow about 4-5 minutes for the chocolate to melt, then spread it out evenly.
Top with toffee pieces, sprinkles, or other toppings.
Allow the candy to cool, then chill in the refrigerator for about one hour.
To pop the candies out of the muffin tin, carefully insert the tip of a sharp knife on one side of the candy and press in until it pops loose.
Notes
Only have one muffin tin? Make them in two batches, using half the butter and brown sugar for each round.The chocolate melts from the heat of the cookies, so there's no stove or microwave step for it.If you don’t have a candy thermometer, drip a little of the boiling mixture into a glass of cold water near the end of the 2-3 minute boil (with the pan off the heat). It’s ready when it turns hard and snaps instead of bending.