Using a handheld mixer or stand mixer, beat butter and sifted powdered sugar for 3 minutes until light and fluffy. Add egg yolks, one at a time, mixing well after each addition. Mix in salt and coconut extract. Add flour and mix until just combined. Don't over mix.
Using your hands, form dough into a ball and slightly flatten to form a disc. Cover with cling wrap and place in refrigerator for 30 minutes.
Grease 8, 4 inch tart pans with butter and place on a baking tray with sides to prevent them from sliding off.
Once dough has chilled and firmed up, knead a few times and roll out the pastry on a lightly floured surface until about ¼ inch thick. Cut the pastry out in rounds using a round biscuit cutter that is slightly bigger than your tart tins (to allow the pastry to go up the sides and slightly overhang the edges). I used a 4½ inch sized cutter. Gently press it into the edges of the tins. Place in refrigerator for another 30 minutes.
Preheat oven to 350°. Line the pastry filled tart pans with parchment paper and fill with baking beans or uncooked rice. Bake for 15 minutes, then remove the parchment and baking beans. Brush with lightly beaten egg and return to the oven for another 10 minutes, or until a light golden brown. Set aside to cool in the tins. Trim off the edges of the pastry that has overhung the tins using a serrated knife.
Remove from tart tins once cooled and set aside.