Preheat oven to 325°. Butter and flour a 9x13-inch baking pan. In a small saucepan, melt together the butter and coarsely chopped chocolate chips with espresso grind coffee over simmering water. Stir occasionally; remove from heat and let cool.

In a large bowl, stir the eggs, sugar and vanilla. Stir the melted chocolate mixture into the mixture in the bowl. Then mix in the flour and salt. Fold in the walnuts and chocolate chips. Pour the batter in the prepared pan and bake 30 to 35 minutes or until a toothpick inserted in the center comes out clean. Allow to cool completely.