1. In large bowl, with mixer at high speed, beat egg whites and cream of tartar until soft peaks form. Beating at high speed, sprinkle in 1/2 cup sugar, 2 tablespoons at a time; beat until sugar is dissolved and whites stand in stiff peaks.
2. Preheat oven to 350°F. In another large bowl, with mixer at medium speed; beat 1 1/2 cups sugar and egg yolks with flour, coffee, baking powder, vanilla extract, and salt until light and fluffy. With rubber spatula or wire whisk, gently fold flour mixture and nuts into beaten egg whites just until blended.
3. Pour batter into ungreased 10-inch tube pan. Bake 1 hour to 1 hour and 10 minutes, until cake springs back when lightly touched. Invert cake in pan on funnel or bottle; cool completely in pan. With metal spatula, carefully loosen cake from pan; place on cake plate.