Make the crust: In a small bowl, whisk together flour and baking powder; set aside. In a large bowl, using an electric mixer, beat butter and sugar until light and fluffy. Add egg and almond extract; beat until combined. With mixer on low, add flour mixture; mix just until combined.
Using an offset spatula or table knife, spread dough in a 9-inch removable-bottom tart pan, evenly covering bottom and sides. Freeze for 20 minutes.
Meanwhile, preheat oven to 350, and make filling: In a large bowl, using an electric mixer, beat butter and 1/4 c sugar until light and fluffy. Add egg and lemon zest; mix until combined. With mixer on low, add flour and then cream; mix just until smooth (do not overmix). Set aside.
In a medium bowl, toss apple with lemon juice; arrange evenly in tart pan over chilled dough. Spread filling over apple; sprinkle with almonds and remaining 1/4 c sugar. Place tar pan on a rimmed baking sheet; bake until golden and set, 40 to 45 minutes. Cool completely on a wire rack.