In a large saucepan over medium high heat, combine the sugar, half and half, butter, baking soda and vanilla.
Stir the mixture until boiling and the sugar has disolved completely. Turn the heat to medium low and continue stiring until the mixture reaches 238 - 241 degrees on a candy thermometer or soft ball stage. (The mixture will begin to take on a light caramel color.)
Stir in the pecans and remove from the heat. Stir the mixture until it begins to thicken and becomes creamy.
Using a tablespoon, drop onto parchment paper, a butter pan or silicone baking mat. Let it cool completely.