In a microwave safe bowl, combine brown sugar, maple syrup, butter, and corn syrup. Microwave uncovered on high for 3 1/2 minutes or until sugar is dissolved and corn syrup is bubbly. Stir in vanilla, baking soda, cinnamon, and salt. Microwave on high 30 seconds longer or until the mixture begins to foam.

In a large bowl, combine cereals and pecans, if using. Add syrup mixture and toss to coat. Transfer to two greased 15 x 10 x 1 inch baking pans.

Bake at 275º uncovered, for 45 minutes, stirring every 10 minutes. Watch carefully, mixture burns easily. Remove from oven and cool on waxed paper. Store in an airtight container.