Eat the tops now and they will replenish with side shoots and keep flourishing . Mine never make it to more than 2 inches as I cant resist eating them!
Quote (from the RHS, where they know a thing or two about gardening):
"Keep plants bushy and productive by pinching the tips of branches regularly and remove any flowers that start to develop".
Basil, not really my forte but pinching out the tips, should encourage bushier plants. The tips themselves will provide the extra bonus of a delicious garnish, far to good to waste.