Preheat oven to 350°F. In large bowl, combine tahini and brown sugar. Add flax egg, lemon extract, and lemon zest. In medium bowl, combine flour, baking soda, baking powder and salt. Add dry ingredients to tahini mixture and combine. Mixture will be crumbly. Fold in white chocolate chips if desired. Press mixture into 8x8 baking pan and bake for 25-30 minutes or until edges are golden brown. Let cool for 5-10 minutes and cut into 9 bars.
optional: Combine 1/3 cup melted white chocolate and 1 tablespoon of lemon juice and drizzle over top of bars.
To make flax egg, combine 1 tablespoon of ground flaxseed and 3 tablespoons of water. Let sit for 5 minutes and add as directed