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Put the butter and both sugars in a large bowl and whisk using electric beaters until light and fluffy. Add the whole egg and egg yolk, then mix thoroughly, scraping down the sides of the bowl to make sure everything is combined. Add the almond and vanilla extracts, and mix to combine.
Tip in the flour, baking powder, bicarbonate and salt, and mix until it forms a dough. Keep mixing until you don’t have any more pockets of flour. Knead in the chocolate chips.
Heat the oven to 180C/160C fan/gas 4. Divide the mixture into 26-28 equal balls of around 40g each. Arrange on a large baking tray and leave to chill for at least 1 hr in the fridge. Can be made a day ahead and chilled overnight. Line two baking trays with baking parchment and arrange the cookies on them, leaving 5cm space between each so they can spread. Bake one tray of cookies on the top shelf for about 15-17 mins until crisp and golden, then remove from the oven and bake the second tray. Leave to cool completely on the trays.
To make the filling, put the jam in a bowl with the finely grated white chocolate and mix well to combine.
Once the cookies are cool, you’re ready to sandwich them. Top the flat side of each with a thin layer of the jam filling, then sandwich with another. You should have 13-14 cookie sandwiches in total. If you have time, chill for a further 30 mins for the filling to set, then serve.