In a good sized saucepan, melt butter and chocolate chips over low heat, stirring, until smooth. Remove from the heat and stir in both sugars. Let cool for a few minutes, then add eggs, one at a time, stirring after each addition. Stir in vanilla, flour and salt. Add nuts.
Spread batter in a greased 9x13 pan. Bake in an oven, preheated to 325°, for about 45 minutes. A toothpick inserted near the center should come out almost clean.