Beat first 6 ingredients at low speed with an electric mixer 30 seconds or just until moistened; beat at medium speed 2 minutes.
Stir in 2 cups semisweet chocolate morsels; pour batter evenly into 2 greased and floured 9-inch square cake pans.
Bake at 350° for 25 to 30 minutes or until a wooden pick inserted in center comes out clean. Cool completely in pans on wire racks.
Microwave white chocolate morsels in a glass bowl at HIGH 30 to 60 seconds or until morsels melt; stirring at 30-second intervals until smooth. Drizzle evenly over cakes; repeat procedure with remaining cup of semisweet morsels. Sprinkle cakes evenly with pecans.