This sticky-sweet cake stars apples in three forms: Applesauce and fresh apples are baked into the cake and an apple cider glaze finishes off the fruity fall dessert.
Preheat oven to 325 degrees. Butter a 9-inch square metal baking pan and line with parchment, leaving a 2-inch overhang on 2 sides.
Whisk together flour, baking powder, cinnamon, and salt. In a large bowl, with a mixer, beat butter and 1 1/2 cups brown sugar until fluffy. Add vanilla and eggs; beat until combined. Reduce speed to low; add flour mixture in 3 additions, alternating with 2 additions applesauce, and beat until combined.
Transfer batter to pan and smooth top. Arrange apples in 3 rows on top, overlapping slightly. Bake until a toothpick inserted in center comes out with a few moist crumbs attached, 1 hour 15 minutes. Transfer pan to a wire rack and let cool 20 minutes.
Meanwhile, in a medium pan, cook cider and remaining 1/4 cup brown sugar over medium-high until thick and syrupy, 15 to 18 minutes. Using parchment, remove cake from pan. Brush glaze over top and sides and let sit until set, 1 hour. (Store, wrapped in plastic, at room temperature, up to 3 days.)
Top Swap We like the firm texture and tart flavor of Granny Smith apples on this cake; Gala, Honeycrisp, and Jonagold apples will also work well.