Line a baking sheet with parchment paper or a silicone baking mat. Set it aside. Pan roast the pistachios until they're lightly toasted. Let them cool, chop them and set them aside.
Add 1 cup of sugar to a skillet.
Turn the heat to medium, let the sugar start to lightly caramelize. Don't stir the sugar but allow it to melt & turn light amber . The sugar needs a large pan so that it all fits in one smooth layer.
As the sugar starts to melt at the edges of the pan, take a heat-proof spatula and push it toward the center of the pan.
Keep pushing the sugar toward the center as it melts and watch the sugar, as you don't want it to burn.
When the caramel has liquified and burned amber, CAREFULLY pour it onto the parchment paper or silpat mats in long streaks.
Smear the sugar out moving quickly. This stuff hardens damn fast!
Scatter the pistachios on top of the hot caramel.
Add the sea salt flakes.
Let it cool & set. This does not take long! If you're not using it right away, store in a cool dry place, not the fridge. Break off the pieces you plan on using , decorate the dessert as you wish.