Measure the butter and cream (separately) and set aside until you need them.
Heat the sugar in a medium, heavy-bottomed pan over medium-high heat without stirring. When it starts to melt, you can give the pan a little shake every so often, so the sugar melts evenly, but do not stir the caramel. Look out for wisps of smoke - it's important not to burn the caramel!
Cook the sugar until it is completely fluid and has become dark, golden brown. If you like your caramel a little bitter, cook the sugar until it is very dark, but be aware that sugar at this temperature can change from broody to burnt in a matter of seconds.
When the sugar is ready, take the pan off the heat and add the butter, stirring until it has been incorporated. Add the cream.
Return to the hob and cook again, now over medium heat, until the caramel is silky and smooth, with no lumps. Remove from the heat and set aside. If you are struggling to get all the lumps out, but the rest of the caramel looks ready, pass it through a metal sieve before you leave it to cool, instead of continuing to heat and stir.
When the caramel is cool enough to eat, start adding sea salt. It's important that you do this to taste - start with 1/2 teaspoon flaky salt, adding only if you palate requires it. You want to balance the aching sweetness of caramel and add a touch of saltiness to the mixture.
When the caramel has completely cooled, you can assemble the scones.