Position rack in lower third of oven and preheat to 325 degrees. Butter sides of 9" square baking pan with 2" high sides. Fold an 18"x12" piece of foil in half crosswise. Line pan with foil, allowing foil to extend over sides. Butter foil. Stir butter and unsweetened chocolate in heavy saucepan over low heat until melted and smooth. Cool.

Sift flour, cocoa, and salt into a small bowl. Blend both sugars in food processor for 3 minutes. Using an electric mixer, beat eggs and sugar mixture in a large bowl until pale yellow and slowly dissolving ribbon forms when beaters are lifted. Add 2 T raspberry jam and 1/2 t raspberry vinegar and beat one minute. Fold in melted chocolate. Fold in dry ingredients, then nuts.

Spread batter evenly in prepared pan. Bake about 32 minutes. Transfer to a rack. Mix 1/4 c raspberry jam with 1/4 T raspberry vinegar, spread over hot brownies. Cool completely.

Glaze:

Melt chocolate with jam, butter and vinegar in a heavy small sauce pan over low heat. Stirring until smooth. Let stand until cool but still pourable.

Spread glaze over brownies. Let stand until chocolate sets. Lift brownies from pan using foil sides, cut into squares.