Begin by preheating the oven to 350°F (175C/155C Fan) and line your mini muffin pan with mini cupcake cases.
Melt your chocolate until smooth, using a double boiler or microwave (see note) and set aside to cool slightly while you make the crusts and cream cheese mixture.
In a mixing bowl, stir together the Oreo crumbs and butter creating a moist crumbly mixture. Spoon this out into the prepared liners (about a teaspoon per liner) and then press firmly into the bases.
In another mixing bowl, beat the cream cheese with the sugar. Then add the egg, beating to incorporate.
Add the vanilla and soured cream, again beating until smooth. And finally add the melted chocolate, beating until smooth.
Spoon this out evenly amongst the liners (about a tablespoon for each).
Place in the centre of a preheated oven and bake for about 12 minutes until set.
Remove from the oven and allow to cool in the pan until you're able to handle them. Then carefully remove and transfer to the refrigerator to cool completely - I usually recommend 4 hours.