In a mixing bowl, combine the creamy peanut butter, softened butter, powdered sugar, and 2 teaspoons of vanilla extract. Mix until smooth and creamy. Set aside as you prepare the dough.
In a large bowl, whisk together the flour, cocoa powder, sugar, and salt. Add the cold butter pieces and use a pastry cutter or your fingers to work the butter into the dry ingredients until the mixture resembles coarse crumbs. Gradually add the ice cold water, mixing until the dough comes together.
Wrap the dough in plastic wrap and refrigerate for at least 30 minutes. This will help the dough firm up and make it easier to roll out.
Once the dough has chilled, lightly flour your work surface and roll out the dough to about 1/8 inch thickness. Use a sharp knife or pastry cutter to cut the dough into rectangles, approximately 3 inches by 4 inches.
Place half of the rectangles on a prepared baking sheet lined with parchment paper. Spoon about a tablespoon of the peanut butter filling onto the center of each rectangle, leaving a small border around the edges. Place the remaining rectangles on top and press the edges to seal. Use a fork to crimp the edges for an extra decorative touch.
Preheat your oven to 350°F (175°C). Bake the Pop-Tarts for 20-25 minutes or until they are set and slightly firm to the touch. Allow them to cool completely on a wire rack.
In a medium bowl, mix together the powdered sugar, meringue powder, cocoa powder, and remaining vanilla extract. Gradually add water until you reach a smooth, spreadable consistency.
Once the Pop-Tarts are cool, drizzle the melted chocolate and warmed creamy peanut butter on top. Sprinkle with coarse salt or sugar to add a delightful finish.