To prepare sauce, combine first 3 ingredients in a food processor; process until smooth. Strain through a sieve into a bowl; discard solids. Cover and chill.
To prepare cakes, coat 12 (6-ounce) ramekins with cooking spray; sprinkle evenly with 2 tablespoons granulated sugar. Set aside.
Combine milk and half-and-half in a small saucepan. Bring to a simmer over medium-high heat (do not boil). Remove from heat; add chocolate, stirring until chocolate melts. Add cocoa and vanilla, stirring with a whisk. Pour into a large bowl; cool completely.
Preheat oven to 325°.
Place 1 cup granulated sugar and butter in a medium bowl; beat with a mixer at high speed until light and fluffy. Beat in egg yolks. Add cooled chocolate mixture; beat until blended. Lightly spoon flour into a dry measuring cup; level with a knife. Stir into chocolate mixture.
Place cream of tartar and egg whites in a large bowl; beat with a mixer at high speed until soft peaks form. Gradually add remaining 1/4 cup granulated sugar, 1 tablespoon at a time, beating until stiff peaks form. Gently stir one-fourth egg white mixture into chocolate mixture; gently fold in remaining egg white mixture. Spoon into prepared ramekins.
Place ramekins in 2 (13 x 9-inch) baking pans; add hot water to pans to a depth of 1 inch. Bake at 325° for 33 minutes or until puffy and set. Loosen cakes from sides of ramekins using a narrow metal spatula. Invert the cakes onto 12 dessert plates. Sprinkle evenly with powdered sugar; serve with raspberry sauce.