In a small bowl, combine together flour and sugar. Cut in the cold butter to the flour and sugar using a pastry blender or use your fingers to rub the flour and butter together.
Next, add the beaten egg yolk and milk and combine until the mixture forms a dough. Flatten into a disc and seal with plastic wrap.
Place the dough into the fridge for at least 1 hour.
After chilling, lightly dust the dough with some flour and use a rolling pin to roll out the pastry on a clean non-stick surface.
Use a large round cookie cutter (or wide-mouth mason glass jar lid) to cut out rounds.
Place the cut out rounds into the well of a muffin tin and gently press down and up the sides to form the tart shell.
Use a fork to lightly pick the bottoms of the shell. Return the muffin tin to the freezer to chill for 1 hour. This prevents the shells from shrinking when baking.
Preheat oven to 400°F/204°C.
Place a small piece of scrunched up parchment over top of each muffin tin well and place some pie weights in each well. (I used dried chickpeas but you can use any dried beans as well if you don't have pie weights).
Bake at 400°F/204°C for 10-12 minutes, or until the pastry is firm and lightly golden.
Remove the muffin tin from the oven and place on a wire rack to cool for about 15 minutes. Gently remove the tart shells and leave them to cool completely. You can use a toothpick to assist in removing the tart shells.