From America's Test Kitchen. I have yet to try one of ATK's recipes that wasn't delicious and turned out great. Their instructions are great for beginner or seasoned cooks. Frozen peaches work much better than fresh
Adjust oven rack to middle position and heat oven to 375 degrees.
Line 13x9-inch baking pan with aluminum foil, allowing excess to overhang pan edges. Spray pan with cooking spray.
Process flour, 11/4 cups almonds, granulated sugar, 1/3 cup brown sugar, and 1/2 teaspoon salt in food processor until combined, about 5 seconds.
Add butter and pulse mixture until it resembles coarse meal (some pea-sized pieces of butter will remain), about twenty 1-second pulses.
Transfer 1/2 cup flour mixture to small bowl and set aside.
Press remaining flour mixture firmly and evenly into bottom of prepared baking pan. Bake until golden brown, about 15 minutes.
Meanwhile, toss remaining 1 tablespoon brown sugar with reserved flour mixture. Set aside.
While crust is baking, remove blade from food processor and wipe out workbowl. Pulse peaches and preserves in food processor until mixture has 1/4-inch chunks, about five 1-second pulses (if larger chunks remain, scrape down sides and pulse 2 more times).
Cook peach mixture in large nonstick skillet over high heat until thickened and jam-like, about 10 minutes.
Off heat, add pinch salt, lemon zest, and lemon juice. Pour mixture over hot crust.
Using fingers, pinch reserved flour mixture to create dime-sized clumps and sprinkle over peaches.
Sprinkle remaining 1/2 cup almonds over top and bake until almonds are golden brown, about 20 minutes.
Cool to room temperature, at least 2 hours. Using foil overhang, lift from pan and cut into 24 squares. Squares are best served on day they are baked because the crust can become soggy with time.
To revive, simply place leftover squares side by side (with no spaces in between the squares) on a baking sheet and heat in a 350°F oven until the bottoms are crisp, 10 to 12 minutes. Allow to cool back to room temperature before eating.