Heat oven to 350°F. Grease 2 (8- or 9-inch) round cake pans with shortening; lightly flour. In medium bowl, mix flour, baking soda and salt.
In large bowl, beat brown sugar and butter with electric mixer on medium speed until well blended, scraping bowl occasionally. Beat in vanilla and eggs. Beat in melted chocolate until blended, scraping bowl occasionally. Alternately add flour mixture and water, beating well and scraping bowl after each addition. Pour batter evenly into pans.
Bake 8-inch pans 28 to 38 minutes (9-inch pans 25 to 35 minutes) or until toothpick inserted in center comes out clean. Cool in pans 10 minutes. Remove from pans; place on wire racks. Cool completely, about 1 hour. Fill and frost as desired.