Dough:
Butter and sour cream for the dough should be cold.
In a bowl, mix flour and salt, add pieces of cold butter. Rub your hands into crumbs.
Add cold sour cream and roll the dough into a ball.
The dough should turn out soft, not sticky (if you just failed to assemble the dough, if it sticks or crumbles, on the contrary, you can add 1 tbsp.l. flour or a little sour cream, respectively).
Wrap the dough ball in plastic wrap and refrigerate for 30 minutes.
For filling:
Separate the protein from the yolk (leave the yolk to lubricate the edges of the cookies).
Mix egg white, sour cream, two types of mustard, rosemary in a bowl, season with salt and pepper. Mix thoroughly.
Cut the beets into thin slices, chop the greens.
Roll out the cooled dough on a sheet of baking parchment into a thin layer.
Pour the sour cream and mustard filling into the center, distribute evenly, leaving 2.5-3 cm of the free edge of the dough.
Sprinkle with chopped herbs, lay out the beet slices.
Wrap the edges of the dough over the filling, brush them with beaten egg yolk and sprinkle with sesame seeds.
Bake the galetta in a preheated 180 degree oven for 30-35 minutes until cooked.