Preheat the oven to 180C / 350F / 160C fan forced.
Cream together the butter and sugar until pale and fluffy. This will take a few minutes, so while that’s happening, in a separate bowl mix the flour, salt and baking powder until it is all well dispersed. Add the egg and vanilla to the butter / sugar mix and beat until well combined.
Add the flour mix to the wet mix and beat until just combined. It will start to come together into a dryish, crumbly dough. This is good.
Use your hands to pull all the dough together, then on a well floured surface, roll out to about 6mm thick. Use a cookie cutter ring to cut out 12 rounds. The dough will be crumbly and may break but simply push it back together. Push the rounds into the holes of a 12 hole muffin tin. Place the muffin tin in the fridge to cool while you make the filling.
Fill each cookie dough cup with the jam filling of your choice, not too high as you don’t want it to boil over. Then place in the oven until the edges start to turn golden – around 10 minutes. Take the tray out of the oven and allow the cookie cups to cool slightly in the tin until you are able to handle them, before removing them to a cooling rack to cool completely.
Melt a little white chocolate and drizzle over the tops and allow to set in the fridge.