1. Finely crush cookies. You can use a food processor for this step, or place the cookies in a ziplock bag and roll it with a rolling pin. Seal the bag but leave about an inch open for air to escape. The crust sticks together best when the cookies are crushed finely.
2. Stir the cookie crumbs and melted butter together with a fork. Press crumbs into the bottom and up the sides of the tart molds.
3. Bake the crust for 8 minutes at 350°F. Cool completely before filling.
For the matcha ganache filling:
1. Heat cream until it comes to the boil.
2. Pour over white chocolate chips to melt them and stir until smooth and shiny.
3. Whisk in matcha powder until all the powder is dissolved fully.
4. Set aside and let cool.
To finish, gently pour cooled matcha ganache into tart molds. Let it set in the refrigerator for about 3 hours before serving.