Chop the butter in cubes and mix it in a bowl with the flour, sugar and salt.
Use your fingers to pinch the butter with the dry ingredientes until there are no chunks of butter left and your mix looks like breadcrumbs. You can also do this process on a food processor.
Add the milk and mix using your hands. You can also do this step in a food processor.
Wrap the dough in cling film and let it rest in the fridge for an hour. If you leave it in there longer let it come to room temperatura before stretching it because it will be too solid.
Place everything in a pot and let it cook until it looks like runny marmalade. Let it cool down completely. Be mindful that once cooled down it will double the thickness. If you're only using raspberries it's going to thicken even more because of the pectin present in the rapberries' seeds.
Once the marmalade is completely cold add the lemon juice. If necessary you can also add a bit of water but don't let it be too runny or it will be able to fill the pop tarts.
Stretch the dough until it's 2mm thick. It's best if you stretch one half of the dough at a time. Cut the dough in rectangles of 10cm by 8cm.*
Place the rectangles on a baking tray with silpat or baking paper and form a rectangle of marmalade at te center (roughly a generous tablespoon of marmalade), leaving 5mm uncovered all around the edge.
Paint the border that doesn't have marmalade with milk and place another piece of dough on top. Press down on the edges with your fingers and then with a fork.
Use a toothpick to make 3 diagonal holes in the pop tart so the steam from the marmalade can escape.
Paint the pop tarts with milk.
Take the pop tarts to a preheated oven at 180C for 15min or until lightly golden.
Make sure that the pop tarts are 100% cold before making the glaze or it will melt.
Place the sugar in a bowl and add the milk little by little. Whisk it together and stop adding milk once you have a thick glaze.
Put a bit of glaze on the pop tart using a teaspoon and spread it a bit around using the back of the teaspoon.
Garnish with freeze dried raspberries or sprinkles.
*You can reuse the dough that's left behind after the rectangles are cut but if it dries down too much you need to add a few drops of water to bring it together.