Grease a small pan with butter and line with parchment paper. I use one of these 6x6 inch pans because I like my caramels to be thick, but you could use a bread pan or something similar.
In a medium-sized pot, combine cream and rapadura sugar. The mixture will bubble up quite a bit so make sure there is a lot of room at the top, but you need the mixture to be deep enough to get a good reading with your candy thermometer. If possible, clip your thermometer to the side of the pot, like this. Not only does clipping it mean you don't have to hold it, it also ensures more accurate readings than placing the thermometer in and then pulling it out into cooler air throughout the cooking process.
Bring mixture to a boil and then reduce heat to medium - I set my stove to just a little over the exact medium mark. Stir often, then when the mixture reaches 225°F stir constantly until it reaches 240°F to prevent the caramel from burning. In my kitchen, it takes about twenty minutes from start to finish.
When the caramel reaches 240°F, quickly pour it into your greased dish/baking pan and allow to cool to room temperature. Once the caramel is room temperature, pop it in the freezer for about five minutes to make it easier to cut.
To cut, score the top with squares to make it easy to figure out exactly where to place your knife.
Next, fill a jar with hot water and place the knife inside - I use a butcher knife. Once the knife has warmed for about fifteen seconds, remove and dry it, then run it through a stick of butter to grease both sides before cutting. Cut the first strip you've marked and then continue with the other sections, cleaning and reheating the knife as necessary. Wrap in parchment paper before storing. I store mine at room temperature if they'll be eaten within a few days. For longer-term storage I keep them in the fridge.