To make cookies:
In a bowl, with mixer on medium,beat 1 1/2 cups powder sugar and butter together until smooth. Beat egg and Vanilla, Scraping down sides of bowl. Stir together flour,baking powder, and salt; stir into butter mixture. Stir in pecans. Spoon dough in a row lengthwise along a piece of plastic wrap and, with lightly floured hands, shape into a cylinderical log about 9 inches long and 2 1/2 inches wide. Roll in plastic wrap and freeze until firm enough to slice, at least several hours or overnight.

Preheat oven to 325 F. cut dough crosswise into 1/4 inch thick slices. Place about 1 inch apart on buttered or parchment paper-lined baking sheets. Bake until dry to the touch or slightly brown on the edges, 18-22 minutes. Sprinkle tops of cookies generously with powdered sugar and transfer to wire rack to cool completely .

To assemble:
Soften Ice Cream slightly . Place large Scoop of Ice Cream on a flat bottom side of 1 cookie; top with another cookie. Press gently until Ice Cream comes out to the edges of the cookies. Repeat to fill remaining cookies with Ice Cream . Serve immediately or wrap individually in plastic wrap and freeze for up to a week.