Cream the butter and 1 cup of the sugar until light and fluffy. Add the egg and mix well.
Sift together the flour and cornstarch; add to the creamed mixture and blend well. Mix the walnuts in thoroughly.
Gather the dough into a ball, wrap in wax paper, and chill for 4 to 6 hours.
Roll the dough out to ¼-inch thickness. Using a small heart-shaped cookie cutter about 1½ inches long, cut out the cookies and place on an ungreased cookie sheet. (If you like, use a smaller cookie cutter to make a “window” in half of the cookies.) Chill the cookies for 45 minutes.
Preheat the oven to 325°F.
Bake the cookies until they are evenly and lightly browned, 10 to 15 minutes. Remove and cool on a rack.
While they are still warm, spread the whole cookies with raspberry preserves, using ¼ teaspoon of jam for each. Top each with one of the “window” cookies.
Sift the remaining ¾ cup confectioners’ sugar into a bowl and press the tops and bottoms of the cookies into the sugar to coat.