Melt butter, sugar, water and salt over a low flame, stirring with a wooden spoon.
Meanwhile, line two cookie sheets with parchment and spray with cooking spray. When the mixture starts to boil, turn the heat up to medium. After 15-20 minutes, the mixture has reached 305 F, turn off the heat and add the vanilla, stirring to incorporate. Getting to the exact temperature is very important. If you take it off too early, it won’t harden and remains sticky.
Immediately pour the caramel into two cookie trays and smooth until evenly coated to about 1/4 inch thick. Put the trays in the fridge to let cool for a few hours (or if you’re in a hurry, throw them in the freezer).
Pull the caramel out of the refrigerator once cooled. Melt the chocolate over a double boiler, stirring to combine. Once the chocolate has melted, spread over the caramel in an even layer. Then immediately sprinkle the chopped toasted almonds AND SEA SALT in an even layer. The chocolate hardens v quickly, so do this quickly.
Put the bark back in the fridge to cool overnight. Once hardened completely, you can crack!