Preheat the oven to 350°F (180°C). Line baking sheets with parchment paper or silicone baking mats. Set aside.
Combine the flour, baking soda, baking powder, and salt in a medium-sized bowl and set aside.
Cream the butter, Splenda, and LEAN together in a large mixer bowl until the mixture is light in color and fluffy. Add egg and mix until combined.
Mix the vanilla extract in well.
Add the dry ingredients and mix until the dough is well combined. It will be thick and should not be sticky. Do not over mix. Once it’s well combined, use a rubber spatula to help it come together to form a more cohesive ball.
Create 1 1/2 tablespoon-sized balls of cookie dough. Gently roll into a ball. Set the balls on the baking sheet. (If using a cookie cutter, use the rolling pin to flatten dough. Should be about 1/4 to 1/2 inch thick)
Bake cookies for 7-8 minutes. The cookies will spread, and the centers will look soft but should look done. Remove just before the edges begin to turn golden. Don't over bake. The cookies will be a little puffy when you take them out of the oven but will fall a bit as they cool.
Remove from the oven and cool on baking sheets for 4-5 minutes before transferring to a wire rack to cool completely.