Add 2 split vanilla beans to 6 cups of granulated white sugar in a sealed container. Shake or rotate twice weekly for about 1 month. Replenish sugar as needed. Leftover sugar lasts for weeks.
We use a full 5 lb. bag of sugar, 4 split vanilla beans, and extend the time to 2-3 months.
Tip: If you do this in a Passover friendly container, not only will you have homemade vanilla sugar for baking, but you will save money too.
Most rabbinical authorities agree that plain granulated sugar and raw vanilla beans are considered kosher for Passover. Check with your Rabbi.