Ideally using a stand mixer with the paddle attachment, mix the butter, caster sugar and light brown soft sugar together until fluffy and paler in colour. This will take 3-5 minutes in an electric mixer (I use speed 3)
Add the egg and vanilla extract and mix in
Add the plain flour, baking powder, bicarbonate of soda and salt and mix them in until just combined
Mix in the white chocolate chips and chopped pistachios briefly, just to evenly distribute them
Divide the dough into 12 portions, use scales for accuracy if you like. Roll each portion into a ball using the palms of your hands, then flatten the dough out into your hand. Place a teaspoon (around 7-10g) of the pistachio cream spread into the centre of the flattened out piece of dough. Fold the dough around the pistachio cream spread and pinch the dough together to seal the pistachio cream spread inside the dough. Roll it back into a ball shape
Do the same with all of the dough until it is used up. Then put all of them into the freezer for 30 minutes. You can either place the balls of filled cookie dough onto a lined baking tray, or into a tupperware container lined with baking paper
Meanwhile, pre-heat your oven to 180C Fan/200C/400F/Gas Mark 6. After the 30 minutes is up and your oven is pre-heated, place the frozen dough balls onto lined baking trays, leaving space (at least 2") between them to spread. If you don't have enough baking trays, keep the dough in the freezer and bake the cookies in batches
Bake for 12-14 minutes, remove from the oven and leave the cookies to cool for at least 10 minutes on the baking trays before moving to a cooling rack
Enjoy warm, or leave to cool fully. Store leftovers in an airtight container and eat within 3 days
Video
Notes
Make sure all your ingredients (particularly the butter and egg) are at room temperature before you start baking.
I prefer to use unsalted butter for this recipe, but you can also use a baking spread.
I recommend using light brown soft sugar for delicious flavour and a more gooey cookie, but you can replace it with caster sugar if you can't get hold of light brown soft sugar.
You can use either white chocolate chips or a chopped up white chocolate bar for the cookies.
Although I provide cup measurements, I highly recommend weighing your ingredients out using digital kitchen scales. It is the most accurate way to measure ingredients and will ensure the best results. Digital scales are very low cost and can be purchased for around £12 ($16.50) .
For teaspoon (tsp) and tablespoon (tbsp) measurements, please use measuring spoons and not the type of spoons you eat with. Again this will ensure accuracy and provide the best results.