Preheat the oven to 180 C (350 F) and grease a 9 or 10 inch tart with removable base. Make sure the tart tin has high sides, at least 1½ inches. To make the base, blitz the Oreos in a food processor to make a fine crumb. Mix in the melted butter. Press the cookie crumb evenly into the sides and base of the prepared tart tin. Refrigerate. To make the filling, melt the chocolate and butter together in a heatproof bowl set over a pot of simmering water. Stir occasionally until the mixture is smooth and combined. Meanwhile, whip the eggs and brown sugar together using a stand mixer fitted with whisk attachment for about 5 minutes, until light and creamy. Gently fold the egg mixture into the chocolate mixture. Then fold in the cream. Pour this mixture into the Oreo crust, stopping short about 1cm from the top of the crust. Bake for 35 - 40 minutes, until puffed and just set. Allow to cool completely, then dust with cocoa. Refrigerate. To poach the pears, bring the sugar, water, vanilla and cinnamon to the boil in a medium pot. Place the pears into the boiling syrup, and cover the surface of the syrup with a disc of baking paper. This will keep the pears submerged so they cook evenly. Poach the pears in the syrup for 20 minutes, or until a paring knife inserted in the base inserts easily. Remove the pot from the heat, discard the baking paper disc, and allow the pears to cool in the syrup. Refrigerate. Once fully cool, cut the pears into halves or quarters, and arrange on top of the tart. Some edible flowers or wired and taped roses can add beautiful colours. Keep refrigerated. Serves 10 - 12. Happy baking!