Coat an 8-inch-square pan with nonstick cooking spray; set aside.

Whisk flour, cocoa, and salt together in a bowl to aerate and combine; set aside.

Place butter in the bowl of an electric mixer and beat with a flat paddle on medium-high speed until creamy, about 3 minutes. Add sugar gradually and continue beating on high speed until light and fluffy, scraping down the bowl once or twice. Beat in vanilla extract.

Turn the machine off, add about one-third of the flour mixture, then beat at low speed. Gradually add the remaining flour, mixing just until blended, scraping down the bowl once or twice. Pat crust into an even layer in the prepared pan. Refrigerate 30 minutes or overnight, if desired.

To bake crust, preheat oven to 350°. Bake about 40 minutes, or until completely dry to the touch; the edges might be slightly darker than the center. Place the pan on a rack to cool, about 5 minutes.

Spread cranberry sauce evenly over crust using a small offset spatula or the back of a spoon.

Place egg whites in a clean, grease-free bowl and whip with a balloon whip attachment on high speed until foamy. Add cream of tartar and whip until soft peaks form. Add sugar gradually and whip until stiff, but not dry, peaks form. Beat in vanilla extract. Spread meringue evenly over cranberry layer. Use the back of a teaspoon to make peaks and swirls in the meringue.

Bake about 25 minutes or until me-ringue is a light golden brown. Place the pan on a rack to cool. Cut into 4x5-inch bars. (Bars may be stored at room temperature in an airtight container up to 2 days).