Crush 100 g Oreos in a food processor (that is about 10 cookies). Melt the butter in a small saucepan. Combine melted butter and crushed cookies. Spread mixture on the bottom of a springform pan and chill in the freezer.
Soak the gelatin sheets in cold water. Warm the milk on the stove and remove just before it reaches boiling temperature. Squeeze the gelatin and add it to the hot milk. Stir to mel and let cool to room temperature.
Combine cream cheese and powdered sugar and mix at medium speed for a couple of minutes. Add the vanilla and mascarpone and mix to combine. Add the milk and gelatin mixture when it's at room temperature and stir to blend.
Chop about 10 cookies with a knife and fold them into the cheese mixture. Take the cookie base out of the freezer and pour in the cheesecake mixture. Chop the remaining cookies into larger pieces and top the cheesecake with those cookies as decoration. Refrigerate overnight or for a minimum of 5 hours.