Preheat oven to 400° F. Cover 2 sheet pans with parchment paper and set aside.
Allow frozen puff pastry to thaw at room temperature for 20 minutes, or until you can easily unfold it.
Unfold one sheet of the puff pastry on a lightly floured surface. Keep the other sheet cold in the refrigerator until ready to use Gently roll it out a bit, mostly to get the seams smoothed out.
Cut into nine roughly square pieces. You can use a small roller to "square them up" but don't go crazy. This isn't MasterChef. Things can be "rustic".
With a small paring knife, score about a 1 cm border along the edge of each square. Don't cut all the way through, just a light scoring.
Place 1 teaspoon of lemon curd in the center of each square. Top with 3 slices of peach, shingled all pretty-like.
Lightly brush the edges of each future tartlet with your egg/milk mixture. Sprinkle each corner with coarse or Swedish sugar.
Put these tartlets in the refrigerator while you prepare your pinwheels. Ooh! Fancy!
Take out your second sheet of puff pastry and roll and cut it into 9 pieces, just like you did with the previous sheet, but do not score the edges.
Place about 1 teaspoon of lemon curd in the center of each pastry piece. Top with 1 tbs of diced peaches. Repeat with the other 8 squares.
Using your small paring knife, cut into each corner of your pastries, just until you get close to your filling, but not all the way into the filling. You'll have 4 sail shaped wedges in each pastry.
Fold the left corner of each "sail" across the the base of the next "sail" as pictured. Repeat with the other 3 corners of each pastry.
Brush the pastries with egg/milk wash and sprinkle with coarse or Swedish sugar. Top off each pastry center with a few more pieces of diced peaches.
Place sheet trays in your oven on the middle two racks. Bake your tartlets in a 400° oven for 18-20 minutes, or until golden brown on the edges. Halfway through baking, swap the tray positions and turn trays, ensuring an even bake.
Cool for 10 minutes, while warming your apricot jelly. Place jelly in a small bowl and microwave for 20 seconds. Stir and heat for another 20 seconds.
Brush tops of fruit only on each tartlet. This will give each baby tartlet a beautiful gloss and enhance its peachiness, while giving it a nice tartness. Tartness...tartlet...get it?! Eat now. Laugh later.