In a large bowl, whisk together flour, powdered sugar, and salt.
Add the grated cold butter, beaten egg, and vanilla extract. Mix until the dough resembles coarse crumbs.
Gradually add cold water, 1 tablespoon at a time, mixing until the dough comes together.
Divide the dough in half, shape into rectangles, wrap in plastic wrap, and refrigerate for at least 30 minutes.
On a floured surface, roll out each dough half into a 9x12-inch rectangle. Trim edges and cut each into nine 3x4-inch rectangles.
Place 9 rectangles on a parchment-lined baking sheet. Brush edges with beaten egg.
In the center of each, place 1 tablespoon of peanut butter and 1 tablespoon of jam.
Top with remaining dough rectangles, pressing edges with a fork to seal. Poke holes on top to allow steam to escape.
Brush tops with beaten egg and refrigerate for 30 minutes.
Preheat oven to 350°F (175°C).
Bake for 30-35 minutes until golden brown. Let cool on a wire rack.
Optional Glaze:
1 cup powdered sugar
1 tablespoon strawberry jam
1 teaspoon lemon juice
1-2 tablespoons milk
Chopped salted peanuts for garnish
To make the glaze:
Whisk together powdered sugar, strawberry jam, and lemon juice.
Add milk as needed to achieve a thick but pourable consistency.
Drizzle over cooled pop-tarts and sprinkle with chopped peanuts. Allow glaze to set before serving.