In small saucepan over medium heat, bring cherries, granulated sugar and lemon juice to simmer, mashing cherries with potato masher or fork to break up. Simmer, stirring frequently, for about 15 minutes, or until mixture thickens. Transfer to shallow container, cover and refrigerate until cold.
In large chilled bowl, fold cherry mixture into ice cream until blended. Cover and freeze about 2 hours, or until firm.
Heat oven to 350 F. Line 2 large baking sheets with parchment paper.
Meanwhile, in medium bowl, combine confectioners’ sugar, cocoa powder, egg whites and salt. Using electric hand mixer on low speed, beat for about 1 minute, or until just blended. Fold in walnuts.
Immediately drop 16 mounds of batter onto prepared baking sheets, spacing evenly. Spray underside of spoon with cooking spray and spread mounds into 2 1/2-inch rounds. Bake 10-12 minutes, or until tops are shiny and cracked. Cool cookies completely.
Scoop ice cream onto flat side of half of cookies. Place another cookie on top of ice cream and gently press down until ice cream spreads to edges. Return sandwiches to freezer for about 30 minutes to firm up before serving.
Note: Brookies can be baked up to 1 day ahead, stored airtight at room temperature.