In a blender or food processor, combine almonds and the 2 tablespoons sugar. Cover and blend or process till nuts are ground. Transfer nut mixture to a medium bowl. Stir in flour, cornstarch and salt. Set aside.
In a large mixing bowl, beat butter with an electric mixer on medium to high speed for 30 seconds. Add the 2/3 cup granulated sugar. Beat about 3 minutes or till very light and fluffy, scraping sides of bowl occasionally. Beat in egg yolks and vanilla till combined. Beat in as much of the flour-nut mixture as you can with the mixer. Using a wooden spoon, stir in any remaining flour-nut mixture.
Form dough into a ball (dough may seem crumbly, but will come together when worked with hands). On a lightly floured surface, roll half the dough at a time till 1/8 inch thick. Using a 2-inch cookie cutter with scalloped edges, cut dough in shapes. (If you like, using 1-inch cutters, cut small shapes from the centers of half of the cookies; these will be cookie tops when assembled). Reroll scraps. Place 1 inch apart on ungreased cookie sheets.
Bake in a 375 degree F oven for 7 to 9 minutes or till edges are very lightly browned. Transfer cookies to a wire rack; cool. Makes about 45 sandwich cookies.
To assemble, spread a scant 1 teaspoon preserves on bottoms of half of the cookies. Top with remaining cookies, bottom sides down. Just before serving, generously sift powdered sugar on top.