Heat oven to 180C/fan 160C/gas 4. Line the base of a 25cm springform tin with baking parchment. Blend butter and biscuit crumbs. Press onto the base of the tin, bake for 10 mins, then cool.
Increase the oven temperature to 240C/fan 200C/gas 9. Beat the cheese and sugar with an electric whisk until smooth, then whisk in the flour, vanilla, 2 tbsp Tia Maria, eggs and 285ml soured cream.
Grease sides of the cake tin with butter. Pour in the mixture and smooth. Bake for 10 mins, then turn oven down to 110C/fan 90C/ gas ¼ for 25 mins. Turn off the oven, then open the door and leave to cool inside the oven for 2 hrs. Don’t worry if it cracks a little.
Mix 142ml soured cream and Tia Maria, then smooth on top of the cheesecake. Chill.