1. Combine flour and salt in a bowl. Spoon through a funnel into a 1-quart (4-cup) wide mouth clean glass jar with lid, pushing mixture through funnel with a straw or fork handle. VERY FIRMLY tap jar a few times after EACH ingredient addition to settle into layers so everything will fit. Repeat process with 6 tablespoons unsweetened cocoa, 3/4 cup granulated sugar, the brown sugar (firmly packed into jar with a spoon), remaining 3/4 cup granulated sugar, 6 tablespoons cocoa, the walnuts, white chocolate chips, and semisweet chocolate chips. Close lid.To bake::
2. Heat oven to 350 degree F. Grease a 9-inch square baking pan. Whisk brownie mix in a large bowl until combined. Stir in 1/2 cup melted butter, 3 large eggs, beaten and 1/2 teaspoon vanilla extract. Spread into pan. Bake 35 to 38 minutes, until a toothpick inserted in center comes out with a few crumbs clinging to it. Cool in pan on a wire rack before cutting. Makes 12 brownies.