Put 375 g flour, 75 g sugar, 250 g margarine in pieces and 4-5 tablespoons cold water into a mixing bowl. First use the dough hooks of the mixer, then work into a short pastry with your hands. Shape the dough into a flat brick, wrap in foil and chill for about 30 minutes.
Preheat oven (electric cooker: 200 °C/circulating air: 180 °C/gas: see manufacturer). Grease a springform pan (26 cm Ø) and dust with flour. 2⁄3 Roll out the dough on a floured work surface until round (approx. 30 cm Ø), place it in the form with the help of the cake roll and press down gently at the edges. Prick the base several times with a fork.
Sprinkle the dough with hazelnuts. Mix the frozen berries with 2 tbsp. flour and spread on the dough base. Roll out the rest of the dough on the sweetened work surface to a circle (approx. 26 cm Ø) and cut into 1-2 cm wide strips. Place as a grid over the filling. Bake in a hot oven for about 50 minutes. Let the pie cool down.