To Make Pastry
In a medium bowl, whisk flour, baking powder and salt.
In a food processor, puree cottage cheese. Add sugar, milk, oil, and vanilla and process until smooth. Add flour mixture and pulse 4 or 5 times, just until a clump of dough forms. (The dough will still be quite sticky and hard to work with, so be ready to get dirty). Turn out onto a lightly floured surface and gently knead several times; do not overwork. Press dough into a disk, dust with flour and wrap in plastic wrap. Refrigerate until chilled, at least 1/2 hour. The dough can be made up to two days ahead).
To Make Filling and Bake
Using a food processor or an electric mixer, blend cream cheese with sugar until creamy. Blend in egg yolk, lemon zest and vanilla. (The filling will keep refrigerated overnight).
Preheat oven to 400 degrees F.Cover a large baking sheet with foil. Spray lightly with cooking spray. Set aside.
On a lightly floured surface, roll dough out into a rectangle, about 12 by 6 inches. Transfer dough to prepared foil. Spread cream cheese mixture down center of dough,leaving a margin of 3/4 inches on each side and 1 inch at both ends. Sprinkle blueberries over mixture.
Fold over dough edges towards middle to create a "pocket". In a small bowl, combine egg white and water with a fork. Brush lightly over pastry. Bake Danish for 20 to 25 minutes, or until golden and firm. Transfer to a wire rack and let cool.
To Make Glaze
In a small bowl, combine confectioners' sugar and lemon juice. Stir until smooth. With a spoon drizzle glaze over Danish.