In a small bowl, sprinkle the yeast over the lukewarm water. Stir to combine and let sit until frothy, about 10 minutes.
In the bowl of a stand mixer fitted with a dough hook or a large bowl, combine the flour, sugar, and salt.
Mix in the frothy yeast with water and the 2 tablespoons (30 grams) salted butter to form a soft dough.
On a lightly floured surface, knead the dough until smooth and elastic.
If too dry and crumbly, add a little more lukewarm water. If too sticky to touch, add just enough flour to handle.
Transfer to a large bowl, cover with plastic or a towel, and allow to rise until doubled, 1-2 hours.
Preheat oven to 400˚F (200˚C). Line a rimmed baking sheet with parchment or lightly grease.
On a lightly floured surface, roll the risen dough into a circle about 1/4 inch (6 millimeters) thick.
Using a sharp knife or pastry cutter, cut the circle into 8 equal slices/triangles.
Place a strip of the salted butter along the widest edge of the triangle away from the center.
Roll up the triangle, pinching and sealing the butter inside the bread as you roll, and slightly turn in the ends to form a crescent shape.
Transfer the formed roll to the prepared baking sheet and repeat with remaining triangles.
Cover the baking sheet with a large cloth and allow to rest at room temperature for 30 minutes, until puffed.
Brush the puffed rolls with additional melted butter, and top with a sprinkling of flaky sea salt.
Bake in the preheated oven until golden brown with a crisp bottom, about 18 minutes.
Allow to cool for 10 minutes before serving.