Combine, pecans, white sugar, brown sugar, buttermilk and butter in a good sized pot on top of the stove. Bring to a boil on medium high and cook to soft ball stage. (Soft ball stage means drop a small amount in ice water and it forms a soft ball when you pick it up out of the water and roll between your fingers) You can also use a candy thermometer and cook to 234 degrees.
Remove pot from heat, stir in vanilla extract, cool for a few minutes and beat with a spoon until becomes thick and creamy. Drop by spoonfuls onto wax paper. Makes 12 to 15 pralines depending on size you make them.