Twice a day is recommended.. for a healthier betta smaller frequent feedings is ideal. Twice a day is about what most people can do so it's recommended more often. Depending upon pellet size, 2-3 pellets per meal is fine (based on a 2x daily feeding).. also depends on how big your betta is.. and it's age.
Feeding a bunch at once with a lot of time in between isn't the best.. think of it like us eating a huge meal and then not eating for a couple of days.. then eating another huge meal. That would cause havoc to our system and theirs.
Keep in mind their stomachs are about the size of their eyes, but doesn't mean one pellet is plenty either- their stomachs are designed to stretch some for feeding, it's normal and natural to have a slightly rounded belly after they eat.
Edit: Didn't see you asked until after- when it comes to my pet bettas I use a mix of Omega One Betta Buffet, Atison's Betta, and some flakes created by IBC, homemade and live foods.
It varies on how much I feed based on each fish- my breeding ones are getting more of the higher quality foods/live food a little more often, the others get fed twice a day with the Omega and Atison's, throw in homemade food + live every couple of days.