Ingredients

• Nonstick vegetable oil spray
• 1 1/3 cups buckwheat flour
• 1/3 cup almond flour or meal
• 1 teaspoon kosher salt
• 1 cup (2 sticks) unsalted butter
• 3/4 cup sugar
• 5 large egg yolks
• 1 large egg
• 1 cup raw walnuts
• 1 cup sugar
• 1 large fennel bulb, fronds reserved, bulb cored, thinly sliced
• Zest from 1 lemon, removed in wide strips
• 1 vanilla bean, split lengthwise
• Vegetable oil (for frying; about 4 cups)
• 2/3 cup powdered sugar
• 2 pints vanilla gelato or ice cream
• 1 pint ground cherries or cape gooseberries, husks removed, rinsed, halved (optional)
• A deep-fry thermometer

Instructions

1. Preheat oven to 325°F. Lightly coat a 13x9" baking dish with nonstick spray. Whisk buckwheat flour, almond flour, and salt in a medium bowl to combine.
2. Cook butter in a medium saucepan over medium-low heat, stirring often, until it foams, then browns, 5–8 minutes. Transfer to a large bowl; let cool slightly. Add sugar and whisk until smooth. Whisking constantly, add egg yolks one at a time followed by whole egg, beating after each addition to fully incorporate before adding more. Add dry ingredients and mix until smooth. Scrape batter into prepared dish; smooth top.
3. Bake blondies until lightly browned and center is firm when gently pressed, 15–20 minutes. Transfer dish to a wire rack and let cool. Cut into 16 bars.
4. To make the sundaes: Preheat oven to 350°F. Toast walnuts on a rimmed baking sheet, tossing once, until golden brown, 5–8 minutes. Let cool slightly; place in a heatproof jar or airtight container. Heat sugar and 1 cup water in a medium saucepan over medium, stirring, until sugar dissolves. Let cool slightly; then pour over walnuts. Seal jar and let sit at least 12 hours and up to 1 day. Pour walnuts into a fine-mesh sieve set over a clean medium saucepan and let syrup drain into saucepan, tossing walnuts to shake off excess. Transfer walnuts to a medium bowl. Reserve sieve. Add sliced fennel and lemon zest to syrup; scrape in vanilla seeds and add pod. Bring to a simmer over low heat. Cook, stirring occasionally, until fennel is translucent and tender, 20–25 minutes. Discard pod; let fennel cool in syrup. Fit another medium saucepan with thermometer; pour in oil to come 2" up sides of pan. Heat oil over medium-high until thermometer registers 350°F. Add powdered sugar to walnuts and toss to coat. Place in reserved sieve and shake off excess sugar. Carefully add walnuts to oil and cook, turning with a spider or slotted spoon to prevent sticking, until brown and crisp, about 3 minutes. Transfer to a parchment-lined rimmed baking sheet; let cool. Break up any clumps. Scoop gelato into bowls. Top with ground cherries, blondies broken into large pieces, walnuts, candied fennel, and fennel fronds.
5. Preheat oven to 350°F. Toast walnuts on a rimmed baking sheet, tossing once, until golden brown, 5–8 minutes. Let cool slightly; place in a heatproof jar or airtight container.
6. Heat sugar and 1 cup water in a medium saucepan over medium, stirring, until sugar dissolves. Let cool slightly; then pour over walnuts. Seal jar and let sit at least 12 hours and up to 1 day.
7. Pour walnuts into a fine-mesh sieve set over a clean medium saucepan and let syrup drain into saucepan, tossing walnuts to shake off excess. Transfer walnuts to a medium bowl. Reserve sieve.
8. Add sliced fennel and lemon zest to syrup; scrape in vanilla seeds and add pod. Bring to a simmer over low heat. Cook, stirring occasionally, until fennel is translucent and tender, 20–25 minutes. Discard pod; let fennel cool in syrup.
9. Fit another medium saucepan with thermometer; pour in oil to come 2" up sides of pan. Heat oil over medium-high until thermometer registers 350°F. Add powdered sugar to walnuts and toss to coat. Place in reserved sieve and shake off excess sugar. Carefully add walnuts to oil and cook, turning with a spider or slotted spoon to prevent sticking, until brown and crisp, about 3 minutes. Transfer to a parchment-lined rimmed baking sheet; let cool. Break up any clumps.
10. Scoop gelato into bowls. Top with ground cherries, blondies broken into large pieces, walnuts, candied fennel, and fennel fronds.
11. Do Ahead Blondies can be made 2 days ahead. Store tightly covered at room temperature. Walnuts can be fried 2 days ahead. Let cool; store airtight at room temperature. Fennel can be candied 2 days ahead. Let cool in syrup; transfer to an airtight container and chill.
12. Blondies can be made 2 days ahead. Store tightly covered at room temperature.
13. Walnuts can be fried 2 days ahead. Let cool; store airtight at room temperature. Fennel can be candied 2 days ahead. Let cool in syrup; transfer to an airtight container and chill.