Preheat oven to 325 °F. Cover cookie sheets in parchment paper, Silpat (silicon) baking sheets. Toast the sesame seeds in a heavy skillet over medium heat until they are golden brown.
Beat the brown sugar and butter together in a medium-sized bowl for several minutes until fluffy. Beat in the egg. Whisk together the flour, salt, and baking powder, then add these dry ingredients to the butter, sugar, egg mixture, mix well. Stir in the toasted sesame seeds, vanilla extract, and lemon juice.
Drop by teaspoonful onto prepared cookie sheets, leaving space for the cookies to spread. Bake for approximately 15 minutes, or until the edges are slightly brown. Cool for a minute or two on the cookie sheets. The cookies are much easier to transfer after a few minutes of cooling than straight from the oven.