1. Preheat the oven to 170℃, Gas Mark 3, and have ready a 20cm spring form tin.
2. Crumb 18 of the cookies, either with a food processor or a rolling pin. Mix the crumbs with the melted butter. Press the mixture onto the base, and 4cm up the sides of the cake tin.
3. Beat together the Philly, sugar and vanilla until smooth. Add the eggs, 1 at a time, mixing on low speed after each addition until just blended. Then stir in the flour and soured cream.
4. Roughly chop the remaining 4 Oreos and stir through the filling then pour onto the crumb crust. Bake for 55-60 minutes or until set. Cool completely on a wire rack then refrigerate for at least 4 hours.