Place the natural yogurt in the base of a large jar (I use a 1000 ml jar for this recipe). Pour the heavy cream over the top of the yoghurt and gently stir the two together using a clean spoon.

Place the lid onto the jar and put it somewhere relatively warm for 24 hours. I put my jar in a yoghurt maker set to 25C.

After 24 hours, you will have a jar of thick, cultured cream. You should see a few bubbles and the cream will look like it's been whipped.

Place the jar (with lid on) into the fridge for 24 hours.

Once the jar of cream has been in the fridge for 24 hours, remove it and empty the cultured cream into the bowl of your stand mixer or Thermomix.

Whip the cultured cream for a few minutes, until the cream separates into butter and buttermilk. It will take up to 5 minutes for this to happen.

Place a piece of fine cloth in a bowl and pour the buttermilk over it, adding the butter on top.

Using your hands, squeeze as much of the buttermilk out of the butter by wrapping it in the cloth and squeezing as hard as you can.

Put the strained buttermilk aside and add the butter back into the bowl of your mixer.

Cover the butter with at least 1L of icy cold water and use your stand mixer or Thermomix to wash the butter.

Now, place the cloth over another bowl and pour the water and butter out into it. Use the cloth to strain out the butter by wrapping it and squeezing it as hard as you can.

Repeat the washing of the butter one more time, straining it again through the cloth and squeezing out as much water as you can.

Clean and thoroughly dry the bowl of your mixer and return the clean butter to the bowl.

Add the sea salt and whip the butter until it's pale and creamy.

Transfer the butter to a clean butter bell or jar for storage.