Spray a cookie sheet (18 x 13 inches) with non-stick cooking spray

Bring sugar, syrup, water, and butter in a pan and bring it to a boil

Use a candy thermometer, and stir continuously until it reaches just below hard crack stage, 285-290 degrees.

Remove from heat and quickly stir in baking soda, salt, and vanilla

Pour into well-greased cookie sheet, and before it cools and hardens, push M&M's® Crispy into the top. You basically want to wait about 10 seconds, then start, just be careful not to burn your fingers.

Let the brittle cool completely

Slip a spatula under the brittle when cool, and lift, then crack into pieces

Store in airtight container for up to a week