Direction

1. Preheat oven to 350°F. Coat a 9-inch square baking pan with cooking spray; line pan with parchment paper. Set aside.
2. Cut off and discard ends from 1 lemon. Cut lemon into quarters; remove and discard seeds. Transfer quartered lemon to a food processor, and process until finely chopped, about 1 minute. Measure out 1/3 cup lemon pulp, then discard any excess pulp. Return 1/3 cup pulp to processor.
3. Add granulated sugar, brown sugar, melted butter, and egg; process until smooth and well combined, about 15 seconds. Add flour, baking powder, and salt; pulse until just incorporated, about 5 pulses, stopping to scrape down sides of bowl as needed. Transfer batter to prepared baking pan, and spread into an even layer.
4. Bake in preheated oven until edges are set and a wooden pick inserted into center comes out with a few crumbs, about 30 minutes. Transfer baking pan to a wire rack, and let cool completely, about 1 hour and 30 minutes.
5. Zest and juice remaining lemon to yield 1 teaspoon zest and 2 tablespoons juice. Whisk together zest, juice, and 1 cup powdered sugar in a small bowl until smooth. Add remaining 1/4 cup powdered sugar, 1 tablespoon at a time, if needed to thicken glaze to desired consistency; drizzle glaze over blondies. Cut into bars, and garnish with small lemon slice pieces.