Preheat oven to 350°.
Combine first 5 ingredients in a small saucepan; bring to a boil. Cover, remove from heat, and let stand 15 minutes. Strain milk mixture through a fine sieve into a large microwave-safe bowl; discard solids. Add chocolate chips and butter to milk mixture; microwave at HIGH 20 seconds or until chips and butter melt, stirring until smooth. Cool slightly; add eggs, stirring with a whisk.
Lightly spoon flour into dry measuring cups; level with a knife. Combine flour and the next 5 ingredients (through salt) in a medium bowl, stirring with a whisk. Add flour mixture to chocolate mixture, stirring just until combined. Spread evenly into a 9-inch square baking pan coated with cooking spray. Bake at 350° for 30 minutes or until center is set. Cool 10 minutes in pan on a wire rack. Cut into 20 pieces.