Sift together the flour, salt and sugar into a bowl.
Add in the cubed butter and work between your fingers until the mixture resembles a fine breadcrumb.
Slowly pour in the water until the dough clumps together. Split the dough into two, wrap in cling film and rest in the fridge for 1 hour.
Once chilled, roll out the dough into a rectangle and cut the dough evenly into 8 rectangles.
Spoon the jam onto 4 of the rectangles of dough, and top with peanut butter leaving enough room at the edge for a border.
Top the pastry with the remaining 4 rectangles, crimp with edges with a fork (trimming off any excess if necessary) and poke some air holes in the top. Place them in the freezer for 15m.
Bake at 190C/375F for 25m or until golden. Once cooked, allow to cool.
Mix the icing sugar with milk until you have a slightly running consistency. Spread this on the cooled pop tarts and finish with sprinkles.