Rocky Road Chocolate Cake

INGREDIENTS

• 1 (18.25-oz.) package German chocolate cake mix
• 1 (3.9-oz.) package chocolate instant pudding mix
• 3 large eggs, lightly beaten
• 1 cup sour cream
• 1/3 cup butter, melted
• 1 teaspoon vanilla extract
• 3 1/4 cups milk, divided
• 1 (3.4-oz.) package chocolate cook-and-serve pudding mix
• 1/2 cup chopped pecans
• 1 1/2 cups miniature marshmallows
• 1 cup semisweet chocolate morsels
• Vanilla ice cream (optional)