Set two oven racks near the center and preheat oven to 375°F. Prepare two baking sheets with parchment paper or silicone mats. In a mixing bowl, blend the softened cream cheese, granulated sugar, egg yolk, lemon juice, and vanilla extract on medium-low speed until uniformly smooth. On a floured surface, roll puff pastry into a 16x8-inch rectangle. Divide lengthwise in half, then slice each half crosswise into four equal squares, yielding eight 4-inch squares. For store-bought sheets, gently roll to smooth creases before cutting. Brush the perimeter of each square with beaten egg white. Fold each corner inward by about an inch, pressing lightly to hold shape. Space the folded pastries 2 inches apart on the baking sheets and brush any exposed dough with egg white. Place approximately 1 tablespoon of filling at the center of each pastry. Bake for 15 minutes, rotate trays, then bake an additional 15 minutes or until puffed and golden brown. Let pastries cool slightly on the sheets.

While they cool, mix powdered sugar, milk, and vanilla extract in a small bowl until the glaze is smooth. Drizzle over pastries while still warm.