Start the crust by pulverizing the Oreos in a food processor until they’re a fine rubble. Drop in the soft butter and continue to blitz. While the blade is running pour in the melted butter and continue to process until it’s all well incorporated.
Tumble this mixture out into a fluted tart pan with a removable bottom and press it evenly across the bottom and up the sides. Place in the fridge while you start the filling.
To make the filling & assemble:
Mix the marshmallows and milk in a medium saucepan and place over low heat. Stir regularly until it all melts together—about 5 – 7 minutes.
Once melted, pour the liquidated marshmallow into a heatproof dish.
Beat in the marmalade, orange zest and juice, Cointreau and vanilla extract and set aside until it is completely cooled.
Once the marshmallow mix is completely cooled whip the cream in a standup mixer with the whisk attachment on medium speed until medium-stiff peaks form—about 4 – 5 minutes.
Turn the mixer down to low and pour in the cooled marshmallow mix and beat just until combined.
Scrape down the bottom and sides with a rubber spatula to make sure it’s all evenly incorporated.
If you’re using the food coloring add this in now and whisk just until combined.
Pour the filling into the crust and cover lightly with foil, as not to mar the top, and refrigerate for at least 8 hours, but preferably overnight.
Decorate the top with extra orange zest, fine or in long strips, just before serving if you want—either way, this is delicious!
-You can make this up to two days in advance and just keep it in the fridge.
-You can also make it ahead and freeze it; lay the pie in the freezer, flat and unwrapped, until it's frozen solid. Then wrap in two layers of plastic wrap and freeze for up to 2 months. To defrost, unwrap it and cover it lightly with foil and place in the fridge for 8 hours.