In the bowl of a food processor, pulse together flours and salt. Add butter and pulse until mixture resembles a coarse meal, 10–12 pulses.
Drizzle in ice water, then pulse until just combined. If dough is too dry and not coming together, add in another tablespoon of water.
Divide dough in half and form into 2 disks; wrap tightly with plastic wrap and refrigerate 1 hour or up to 2 days.
Heat oven to 350ºF.
Remove dough from refrigerator and let sit at room temperature 10 minutes. Line a baking sheet with parchment paper.
Roll dough out into a 10x13-inch rectangle on a lightly floured surface.
Trim dough to make a 9x12-inch rectangle then cut into nine 3x4-inch pieces.
Arrange dough rectangles on a prepared sheet spaced 1-inch apart; transfer sheet to freezer.
Repeat rolling and cutting with second dough disk.
Remove sheet from freezer and brush edges of dough rectangles on sheet with egg wash.
Spoon a rounded tablespoon of pumpkin butter into centers of dough rectangles on sheet. Slightly spread pumpkin butter, leaving ¼-inch border.
Place remaining dough rectangles over top of rectangles topped with pumpkin butter.
Lightly press edges to seal, then make indentations around edges of each pop tart with tines of a fork.
Brush remaining egg wash over pop tarts. Then cut 4–5 vents in the top of each pop tart. Bake until tops and edges of pop tarts are golden brown, 30–35 minutes; cool completely on sheet.
Meanwhile, whisk together confectioners' sugar, maple syrup, milk, and salt for the maple glaze.
Spoon or drizzle glaze over cooled pop tarts and sprinkle with turbinado sugar, if using. Enjoy!