Mix 300g of flour with baking powder, baking soda, and salt.

Thoroughly combine 150g of softened butter with sugar and vanilla. Then add the eggs one at a time, ensuring each egg is incorporated before adding the next.

Once the eggs are mixed in, add 1/3 of the sour cream and blend.

Next, add 1/3 of the flour mixture from step 1. Mix until incorporated. Repeat with the remaining cream and flour in two additional rounds. After the last addition of flour, mix minimally and begin preparing the filling.

Combine 40 g of flour, brown sugar, and cinnamon for the filling.

Mix in 50g of softened butter, working it with your hands for best results.

Add the walnuts, slightly chopping them beforehand. Use a knife to keep the pieces larger.

Mix thoroughly to create the cake filling.

Line a baking tray with parchment paper and grease the sides with butter. This recipe requires a large, deep rectangular tray. If you want a smaller portion, halve the ingredients and use a smaller tray.

Pour half of the batter into the tray, spreading it evenly with a spoon. Sprinkle half of the filling over the entire surface.

Pour the remaining batter over and sprinkle the rest of the filling. Place the tray in the oven at 180-200 degrees Celsius.

When the cake is browned and risen, test it with a toothpick.

Remove from the oven and let it cool.

Slice the cake and serve warm or cold.

Enjoy!