Crush the digestive biscuits finely using a food processor or rolling pin.
Mix thoroughly with the melted butter until evenly combined.
Press the mixture firmly into the base of a 23 cm round spring-form tin, creating an even layer.Tip: Use the bottom of a glass to compact the base well - this helps the cheesecake slice cleanly later.Place the tin in the fridge while you prepare the filling.
Make the Cheesecake Filling
In a stand mixer or large bowl, combine: cream cheese, mascarpone, yoghurt, sugar, lemon zest and juice. Mix until smooth and creamy, with no lumps.
Gently fold in the whipped double cream using a spatula.
Whisk in 100 ml of the strawberry jelly - this helps the cheesecake set while keeping it light.
Spoon the mixture into the tin and smooth the surface with a palette knife. Refrigerate for 20–30 minutes to lightly firm up.
Add the Strawberries
Arrange the sliced strawberries evenly over the cheesecake. Press them in gently so they stick, without sinking too deep. Try to cover as much of the surface as possible for an even finish.
First Jelly Layer
Using a ladle, gently pour a thin layer of jelly over the strawberries - just enough to cover them. Pour slowly to avoid disturbing the fruit. Return the cheesecake to the fridge for 30–60 minutes, until the jelly is set.Important: The jelly should be warm, not hot. Hot jelly can melt the cheesecake layer and cause bleeding.
Final Jelly Layer & Blueberries
Once the first jelly layer has set, pour over the remaining jelly. Scatter the blueberries evenly on top.
Place the cheesecake back in the fridge and allow it to set overnight. This resting time is essential for clean slicing and proper structure.
Unmould and Slice
The next day, run a thin knife carefully around the edge of the tin to release the jelly. Remove the springform ring gently. Slice with a sharp knife, cutting straight down, then pulling the blade out towards you. Wipe the knife clean between slices for best results.
Serve
Serve well chilled. Light, creamy, refreshing — this is classic Polish sernik na zimno, just as it should be.