Chocolate cheesecake

Ingredients

• 100 grams plain digestive biscuits
• 2 1/2 tablespoon butter, melted
• 2 tablespoons plain flour
• 1 tablespoon cocoa, sifted, plus extra for top
• 500 grams quark or cream cheese, at room temperature
• 1/2 cup sour cream
• 1/2 cup caster sugar
• 1 teaspoon vanilla extract
• 1 teaspoon lemon juice
• 3 medium free-range eggs, size-6, at room temperature
• 1/4 cup cream
• fresh blueberries or raspberries, optional