Line a square baking pan (see note) with parchment paper.
In a large saucepan, add the half and half and lavender. Bring to a low simmer. Simmer for about 3 minutes, then strain.
Add the cream back to the pot, along with the butter, condensed milk, sugar, and salt (see note).
Over low heat, cook until the butter is melted. Turn the heat up to medium low and cook until it starts bubbling. If using a candy thermometer, attach it to the side of your pot so that you can read it easily.
Stir and cook while the mixture bubbles, watching the temperature as it cooks. Continue cooking until the temperature reaches about 245-250 degrees. Your thermometer may have this marked as “firm ball stage.”
Once you’ve reached this temperature, continue cooking for about 30 seconds or so and turn off the heat. Stir in the vanilla.
Pour the mixture into your prepared pan. Don’t try to scrap any of what’s left in the bottom of the pot; this may result in a grainy texture for the final product.
Lightly tap your pan on the counter to even out the caramel. Let cool for about 30 minutes.
Sprinkle lightly with sea salt and transfer to the refrigerator. Chill for about 2 hours.
Cut into cubes. Store in the fridge or at room temperature.
Notes
Don’t skip the salt in the cooked caramel. You can skip the coarse finishing salt at the end if you are afraid they’ll be too salty, but these are almost pure sugar. You need at least some salt to balance the sweet if you don’t want something sickly sweet.
Do not try to rush this recipe by turning the heat up — you will burn your caramel. It takes the time it takes.
Cook the caramel exactly to the correct temperature. Too low and your caramel won’t set up. Too high and your caramel will be too hard. This is why a thermometer is important — there’s a short window in which you will end up with perfectly, chewy caramels. If you haven’t used your thermometer in a while, test it by bringing a pot of water to boil with the thermometer attached to the pot. When it boils it should read 212 degrees.
A square baking pan will give you caramels that are almost perfectly square. Anything larger will result in caramels that are thin and brittle. Do not skip lining your pan with parchment.
Variations: You can leave the lavender out of these if you’d like; just skip the steeping part. You can use light brown sugar or even white sugar instead of dark brown, but your caramels will not have the deep butterscotch flavor that makes them so good.