Raspberry Brownies

1 cup (2 sticks) unsalted butter
4 ounces unsweetened chocolate, chopped
4 large eggs
1 1/2 cups sugar
1 teaspoon pure vanilla extract
2 Tablespoons raspberry liqueur
1/2 teaspoon salt
1 cup all-purpose flour
1 1/2 cups shelled walnuts, coarsely chopped
1/2 cup mini semisweet chocolate chips
1 cup raspberry preserves
Confectioners' sugar, for dusting, optional

Preheat oven to 350 degrees. Coat a 13X9 inch baking pan with nonstick cooking spray. Melt together butter and chocolate in bowl set over simmering water in saucepan. Stir until smooth. Set aside to cool. Whisk eggs and sugar in large bowl until well combined, about 1 minute. Whisk in the chocolate mixture until blended. Whisk in vanilla, 1 tablespoon of the liqueur and the salt. Stir in flour in 3 additions. Fold in walnuts and chocolate chips. Spread half of batter over bottom of prepared pan. Mix together preserves and the remaining 1 tablespoon liqueur in small bowl. Spread over batter in pan. Place in freezer until preserves are set, about 20 minutes. Spread remaining batter over top of preserves. Bake until wooden pick inserted in center comes out clean, about 45 minutes. Cool in pan on wire rack. Cut into 32 brownies. To serve, dust with confectioners' sugar, if desired.