In the bowl of a stand mixer fitted with the paddle attachment, beat flour, cold butter, and 2 teaspoons (kosher salt) at low speed just until butter is coated with flour. With mixer on low speed, add ice water in a slow, steady stream, beating just until dough comes together, about 1 minute. (There will still be large pieces of butter.) On a lightly floured surface, shape dough into a 6-inch square. Wrap in plastic wrap; refrigerate for 30 minutes.
On a lightly floured surface, roll dough into a 15×8-inch rectangle, lightly flouring the surface and top of dough as needed. Fold dough into thirds, like a letter. Rotate dough 90 degrees; roll into a 15×8-inch rectangle, and fold into thirds, like a letter. Repeat procedure once. Wrap dough in plastic wrap, and refrigerate for at least 1 hour.
Preheat oven to 400°F (200°C). Line 2 rimmed baking sheets with parchment paper.
In a medium bowl, stir together cream cheese, Parmesan, egg yolk, dill, garlic powder, and remaining ¼ teaspoon of kosher salt until well combined.
On a lightly floured surface, roll dough into a 17×10½-inch rectangle. Trim edges to create a 16×10-inch rectangle. Cut rectangle in half lengthwise to create 2 (16×5-inch) rectangles; cut each half into 4 (5×4-inch) rectangles. Using the tip of a small, sharp knife, score a ¾-inch border within each rectangle. Gently transfer dough rectangles to prepared pans, spacing at least 1 inch apart. Freeze for 15 minutes.
Divide cream cheese mixture among dough rectangles (about 2 tablespoons [about 30 grams] each), spreading evenly within scored border; top each with 5 asparagus spears. Brush exposed borders with egg. Sprinkle with everything bagel seasoning.
Bake for 10 minutes. Reduce oven temperature to 375°F (190°C), and bake until puffed and golden brown, 6 to 10 minutes. Let cool on pans for 5 minutes. Top with smoked salmon and Pickled Red Onion.
