Make the crust: In a large bowl, beat butter and sugar together until completely creamy. Beat in egg, vanilla, and almond extract until smooth. Combine flour, baking powder, and salt. Beat flour mixture into liquid until a soft dough forms.
Press into the bottom and halfway up the sides of a parchment paper-lined 9x13 baking dish. Prick dough all over with a fork.
Bake crust at 350F 20 minutes or until just slightly golden. Remove from oven and set aside.
Make the filing: In a large saucepan, combine blueberries, sugar, and lemon juice. Bring to a simmer over medium-high heat then remove some of the liquid and whisk with cornstarch in a small bowl. Stir cornstarch mixture back into blueberries and cook sauce, stirring occasionally until bubbly and thickened. Remove from heat and pour into bottom of crust.
Bake pie at 350F 20-25 minutes or until crust is golden brown and filling is bubbly. Remove from oven and cool completely before cutting into squares. Enjoy!