Mix flour and salt in a large mixing bowl.

Add cold butter and chop finely.

Dissolve baking soda in sour cream.

Add the sour cream to the butter-flour mixture and knead briefly to form a roughly homogeneous shortcrust dough.

Divide the dough into one larger and one slightly smaller piece and chill in an airtight container for 30 minutes.

Cut the unpeeled lemon into pieces and remove the seeds.

Place the lemon pieces with peel in a blender and puree until smooth.

Weigh out sugar and set it aside.

Line the base of the springform tin with baking paper.

Roll out the larger piece of dough on a floured work surface into a circle larger than the springform tin.

Place the circle of dough in the baking tin, pull up a small edge, and sprinkle the base with cornstarch.

Roll out the smaller piece of dough into a circle the same size as the springform tin.

Add the sugar to the pureed lemon and stir briefly.

Spread the lemon filling evenly over the cornstarch-dusted dough base in the springform tin.

Carefully place the second circle of dough on top of the filling and press the edges firmly together.

Prick the cake in several places with a fork.

Bake the Russian lemon pie in a preheated oven at 356 °F (180 °C) for approximately 30 minutes and leave to cool completely.

Cut the lemon cake into pieces and serve.