Preheat oven to 350°F. Prepare mugs with vegetable pan spray and place in 9 in. x 9 in. square pan.
In small bowl, whisk together sugar, flour, cocoa powder and salt.
In large bowl, whisk together oil, milk, egg and vanilla. Add flour mixture and chocolate chips; stir until just combined. Divide evenly between mugs.
Bake 32-34 minutes, or until toothpick inserted in center comes out nearly clean. Cool mugs in pan on cooling grid 15-20 minutes or until mugs are cool enough to touch. Top with ice cream, caramel and nuts, if desired. Serve warm.