In a medium saucepan combine sugar, butter, cream, salt and vanilla. Cook over medium heat stirring occasionally until the syrup reaches the soft ball stage (between 234°F and 240°F). If you do not have a thermometer, drop a bit of the syrup into a glass of cold water and a soft ball should form which flattens when removed from the water and placed on a cold surface.
Once the soft ball stage is reached, quickly stir in the M&Ms and scoop by the tablespoon onto a cookie tray lined with foil or parchment. Spray a cookie scoop with nonstick baking spray for easy scooping.
Let cool and enjoy. Makes about 20 pralines.