1. Preheat oven to 350°.
2. To prepare cake, coat bottoms of 2 (8-inch) round cake pans with cooking spray. Line pans with wax paper; coat wax paper with cooking spray.
3. Weigh or lightly spoon flour into dry measuring cups; level with a knife. combine flour, 3/4 cup cocoa, baking soda, and salt in a medium bowl, stirring with a whisk until blended. Combine buttermilk and 2 teaspoons vanilla in a 2-cup glass measure. Place granulated sugar and butter in a large bowl; beat with a mixer at medium speed until well blended (about 5 minutes). Gradually add egg substitute; beat well. Add flour mixture and buttermilk mixture alternately to sugar mixture, beginning and ending with flour mixture.
4. Pour batter evenly into prepared pans. Bake at 350° for 38 minutes or until cake springs back when touched lightly in center. Invert cakes onto wire racks, and cool completely.
5. To prepare chocolate frosting, place cream cheese and milk in a medium bowl; beat with a mixer at low speed until smooth. Beat at high speed until creamy. Add melted chocolate; beat well. Combine powdered sugar and 1/4 cup cocoa; gradually add sugar mixture to cheese mixture, beating at low speed until blended. Add 1 teaspoon vanilla; beat well 1 minute or until very creamy.
6. Remove wax paper from cake. Place 1 cake layer on a plate; spread with 1/2 cup frosting. Top with second cake layer, spread remaining frosting over top and sides of cake.