Dough:Butter and sour cream for the dough should be cold.In a bowl, mix the flour and salt, add the pieces of cold butter. RUB your hands in the crumb.
Add cold sour cream and collect the dough into a ball.
The dough should be soft, not sticky (if you just could not collect the dough, if it sticks or crumbles, on the contrary, you can add 1 tbsp 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 biscuits).Combine in a bowl of egg white, sour cream, two kinds of mustard, rosemary, season with salt and pepper. Mix thoroughly.
Beets cut into thin slices, green chop.
Roll the cooled dough on a sheet of baking parchment into a thin layer.
In the center pour sour cream and mustard fill, spread evenly, leaving 2.5-3 cm of the free edge of the dough.
Sprinkle with chopped herbs, put the slices of beet.
Wrap the edges of the dough on top of the filling, grease them with beaten egg yolk and sprinkle with sesame seeds.
Bake a galette in a preheated 180 degree oven for 30-35 minutes until ready.