01 - Cut cold butter into flour in a large bowl until mixture resembles coarse crumbs. Incorporate sourdough discard, sugar, and salt until a soft dough forms. Shape into a disk, wrap in plastic, and refrigerate for at least 1 hour.
02 - Beat softened cream cheese in a medium bowl until completely smooth. Blend in granulated sugar, vanilla extract, and lemon juice until creamy and fully incorporated. Set aside at room temperature.
03 - Combine raspberries, granulated sugar, cornstarch, and lemon juice in a small saucepan. Cook over medium heat, stirring constantly, until mixture thickens and bubbles, 3 to 5 minutes. Remove from heat and allow to cool completely.
04 - Preheat oven to 375°F. Line a baking sheet with parchment paper. On a lightly floured surface, roll chilled dough to 1/4-inch thickness. Cut into 8 rectangles or circles. Place 2 inches apart on prepared baking sheet. Create an indentation in center of each piece. Spoon 1 tablespoon cream cheese filling into each center, then top with raspberry filling.
05 - Let assembled pastries rest at room temperature for 20 to 30 minutes until slightly puffed. Brush edges lightly with beaten egg. Bake for 20 to 25 minutes until golden brown and filling is set. Transfer to wire rack to cool completely.
06 - Whisk powdered sugar, milk, and vanilla extract until smooth. Drizzle glaze over completely cooled pastries just before serving.