Preheat your oven to 375 ℉. Spray a 9x13 inch baking dish with nonstick spray and set aside.
In a large mixing bowl, beat together the butter and 1 ½ cups granulated sugar until light and fluffy, about 1-2 minutes.
Add the eggs, vanilla and lemon extract and mix until combined.
In a separate bowl, whisk together the flour, baking powder, salt and lemon zest.
Add 1 tablespoon lemon juice to the milk. Alternate adding the flour mixture and milk mixture into the butter mixture, mixing between additions until fully combined.
Fold in the blueberries without overmixing.
Pour the batter into the prepared baking dish and spread evenly. Bake for 30-35 minutes or until a toothpick inserted in the center comes out clean.
Add the remaining lemon juice and remaining sugar to a medium saucepan. Heat over medium heat until steamy, whisking until the sugar dissolves completely. Remove from heat.
Once the cake is done baking, use a toothpick to poke holes all over the top of the cake. Slowly drizzle the warm lemon glaze overtop the cake.
Allow the cake to cool completely before frosting with Cool Whip.
Top with extra fresh blueberries and lemon slices if desired before serving.