Preheat your oven to 180°C (350°F). Line the base of a springform pan with parchment paper. Lightly grease the sides. This helps the cheesecake release easily later.

Place digestive biscuits in a food processor. Blend until fine crumbs form. If you do not have one, crush them in a zip bag with a rolling pin.

Mix biscuit crumbs with melted butter and sugar. Stir until the mixture looks like wet sand. Press it firmly into the base of the pan.

Bake the crust for 10 minutes. This step helps it stay crisp under the creamy filling. Remove from the oven and let it cool slightly.

Place flour and brown sugar in a bowl. Add cold butter cubes. Rub with your fingers until small crumbs form. Set aside for topping later.

Place cream cheese in a large mixing bowl. Beat until smooth and creamy. This step removes lumps and creates a silky cheesecake texture.

Add sugar and mix well. Then add eggs one at a time. Mix gently after each egg. Avoid over-mixing because too much air can cause cracks.

Add sour cream, vanilla extract, and lemon zest. Stir slowly until the mixture becomes smooth and thick. The batter should look creamy and glossy.

Pour the cheesecake filling over the baked crust. Use a spatula to smooth the top evenly. Tap the pan lightly on the counter to remove air bubbles.

Sprinkle the crumble mixture over the cheesecake filling. Spread it evenly so every slice gets some crunchy topping.

Place the cheesecake in the oven. Bake for about 40 minutes. The edges should look set while the center still jiggles slightly.

Turn off the oven and open the door slightly. Let the cheesecake cool inside for 30 minutes. This prevents cracks and keeps the texture smooth.

Place the cheesecake in the refrigerator for at least 4 hours. Overnight chilling works best. The flavors deepen and the texture becomes perfect.

Remove the cheesecake from the pan. Slice with a sharp knife. Clean the knife between cuts for neat slices.