Add your dry ingredients to a large bowl and whisk to blend them all together.
Dump in the cold butter chunks. (You want your butter cold!) Again, use vegan butter if you are dairy-free.
Use a pastry blender to cut in the butter. (You could use a food processor, but this tends to make the butter pieces too small and you will not get the same flaky layers.) Your flour mixture will look crumbly.
In a small bowl, whisk your wet ingredients together. Pour the wet ingredients into the dry ingredients.
Mix the ingredients the best you can. You don't want the dough too wet so it will take a bit of effort.
I like to do the final mix by hand. It helps to really get the bits of dough all into one ball.
Wrap the dough in plastic wrap and refrigerate for 30-45 minutes. Getting it cold will help you get those flaky layers!
Preheat the oven to 350º F
Layout a piece of wax paper and place the dough ball on top. Optional: sprinkle a little flour on the wax paper to prevent sticking.
Roll the dough to ¼-inch thickness. Use a pizza wheel to cut the uneven edges off. Cut into evenly sized squares or rectangles.
Place jam or filling in the middle of a square. Spread it around but leave a good amount of dough around the edges. This is important so you can seal the edges together.
Place a square the same size over the jam. Use a fork to press the edges down all around the square.
Gently move each pop tart to a parchment paper-lined baking sheet.
Optional: Brush each pop tart with egg wash or milk to allow it to get golden.
Bake at 350º F for 20 minutes until the outside is golden. Your actual bake time will vary depending on the size of your pop tarts so start checking at 18 minutes for the golden color.
Mix the powdered sugar, pure vanilla extract, and milk to make your icing. Drizzle it over the top and decorate with sprinkles if you like.