Heat oven to 450°F.

Spray 12 regular-size muffin cups with cooking spray.

Heat pan in oven 2 to 3 minutes.

In small bowl, mix flour, cocoa and salt.

In medium bowl, beat eggs and milk with whisk.

Add flour mixture and melted butter; beat with whisk just until blended (do not overbeat).

Divide batter evenly among muffin cups (cups will be almost full).

Bake 20 minutes.

Reduce oven temperature to 350°F; bake 15 to 18 minutes longer or until tops of popovers are dry.

Immediately press 1 marshmallow in center of each popover.

Bake 2 minutes longer or until marshmallows are soft.

Remove from muffin cups to serving platter.

In small microwavable bowl, microwave chocolate chips and oil on High 30 to 60 seconds, stirring every 15 seconds, until melted and smooth.

Drizzle over popovers.

Serve warm or at room temperature.