Grape Cake With Hazelnut Streusel

["Preheat oven to 350u00b0F. Butter a 13x9"" pan. Lightly dust pan with flour, tapping out excess. Toast hazelnuts on a rimmed baking sheet, tossing once, until golden brown, 10-12 minutes. Bundle nuts in a kitchen towel and rub vigorously to remove skins. Spread out and let cool.", "Transfer 1 cup hazelnuts to a medium bowl (reserve remaining hazelnuts for the cake). Add brown sugar, 1/2 cup flour, 3 Tbsp. granulated sugar, and 1/4 tsp. salt and mix to combine. Using a fork, mix in 6 Tbsp. melted butter until well combined; set streusel aside.", "Pulse reserved 3/4 cup hazelnuts and remaining 1 1/2 cups granulated sugar in a food processor until nuts are finely ground. Add lemon zest and remaining 1/2 cup room-temperature butter and pulse until combined, about 1 minute. Add eggs one at a time, scraping down sides of bowl as necessary. Add vanilla and pulse just to combine.", "Whisk baking powder and remaining 2 cups flour and 3/4 tsp. salt in a medium bowl. Pulse in half of dry ingredients to combine, then pulse in yogurt. Pulse in remaining dry ingredients until just combined.", "Transfer batter to prepared pan; smooth top. Sprinkle with three-quarters of the grapes. Top with streusel, then sprinkle with remaining grapes. Bake cake on a rimmed baking sheet until a tester inserted into the center comes out with moist crumbs attached, 50-60 minutes. Transfer cake to a wire rack and let cool."]