Place curry powder and flour into a large bowl. Rub butter into flour using fingertips until mixture resembles small breadcrumbs. I used my food processor to quicken the process. Make a well and add egg yolks and water. Mix to form dough. Form dough into a ball and then flatten, cover with cling wrap and place in refrigerator for 30 minutes.
While dough chills, make the filling. In a small bowl, place curry powder, garlic and enough water to form a paste. Over a medium fire, heat canola oil. Add curry paste and onion and cook for 5 minutes, stirring frequently. If the mixture gets dry.
Add chicken thighs, thyme; cook for 10 minutes then add chicken stock. Bring to boil, then lower the fire to a simmer.
Cook for 20 minutes. Remove chicken and shred finely.
To the pot, add 1 tablespoon of flour and 2 tablespoon water and stir to combine, cook for about 2-3 mins until thickened.
Add chicken and scallion into the sauce; mix well. Remove from fire and cool.
Prepare egg wash by mixing 1 egg yolk with 1 tablespoon of water.
While filling cools, remove the dough from the refrigerator. On a lightly floured surface roll dough to 1/8 inch thickness. Cut 3 inch circles (you can use a biscuit cutter or a glass) to fit the tart pans. Place half of the cutout pastries in the pan. Place a spoonful of filling into each patty. Try to fill each patty with the same amount.
Brush ends with egg wash, place the remaining pastry on the top. Go around the edges with a fork to seal. Prick the top with a fork.
Brush tops with egg wash.
Place in oven and cook for 25 minutes or until golden brown. Eat while warm.