Step 1

Preheat oven to 350°. Butter a 13x9x2" metal or glass baking dish; sprinkle bottom evenly with 3 Tbsp. raw sugar. Set aside.

Step 2

Pulse walnuts in a food processor until coarsely chopped. Set 2 cups aside. Add all-purpose flour to processor and pulse until walnuts are very finely ground, 1–2 minutes. Add almond flour; pulse to blend. Set aside.

Step 3

Using an electric mixer, beat 1 cup butter and granulated sugar in a large bowl until light and fluffy, 2–3 minutes. Add eggs, cream, yogurt, and salt. Scrape in seeds from vanilla bean (reserve bean for another use). Beat until well combined, 1–2 minutes. Add ground-walnut mixture and beat just to blend. Gently fold in chopped walnuts, being careful not to overmix. Pour batter into prepared dish; smooth top. Sprinkle with remaining 3 Tbsp. raw sugar.

Step 4

Bake until cooked through and a tester inserted into center comes out clean, 50–55 minutes. Let cool in pan on a wire rack. Serve with whipped cream. DO AHEAD: Can be made 3 days ahead. Cover and chill. Cake is best served cold.