Preheat oven to 275 degrees. Cut 4 vanilla beans into 1/2" pieces and grind to a coarse powder in a coffee grinder. In a large bowl, mix the sugar, beans and extract until thoroughly combined (when the extract is completely incorporated the mixture will look a bit like dough).
Pour the sugar mixture into a 8" x 8" pan, spread out evenly to a 1/2" thickness and press it down lightly. Next, use a knife to score out 1/2" by 1/2" cubes by running the knife the length of the pan every 1/2" and the width of the pan every 1/2". Bake in the oven for 1 1/2 hours.
Remove from oven and let cool. Once cooled, carefully flip the pan over onto a bigger cookie sheet to remove the sugar. Gently break into cubes along the scored lines. To “round” the edges of the cubes gently pour them into a big pot with a cover and lightly shake. Check and repeat if necessary. Next pour the cubes from the pot and into a small holed colander or sifter to gather the cubes and sift off any sugar particles that can be reserved as granulated vanilla bean sugar!