Butternut Squash Coffee Cake

Preparation

1. Streusel

   Step 1

   Whisk ½ cup (63 g) all-purpose flour, ¼ cup (50 g) granulated sugar, 1 Tbsp. pumpkin pie spice, and 1 tsp. Diamond Crystal or ½ tsp. Morton kosher salt in a medium bowl to combine. Add 4 Tbsp. chilled unsalted butter, cut into ½" pieces, and work into dry ingredients with your fingers until pea-size clumps form. Chill streusel until ready to use.

2. Spice Mixture

   Step 2

   Whisk ⅓ cup (67 g) granulated sugar, 2 Tbsp. all-purpose flour, 1 Tbsp. pumpkin pie spice, and ½ tsp. Diamond Crystal or ¼ tsp. Morton kosher salt in a small bowl to combine; set spice mixture aside.

3. Cake and Assembly

   Step 3

   Place a rack in middle of oven; preheat to 375°. Lightly coat an 8x8" metal baking pan with vegetable oil. Line with parchment paper, leaving overhang on 2 sides. Vigorously whisk 2 cups (250 g) all-purpose flour and 2 tsp. baking powder in a large bowl to combine.

   Step 4

   Blend 3 large eggs, 3 cups 1" pieces peeled butternut squash (about 10.5 oz./300 g), 2 cups (400 g) granulated sugar, 2 tsp. Diamond Crystal or 1¼ tsp. Morton kosher salt, 2 tsp. pumpkin pie spice, 2 tsp. vanilla bean paste or vanilla extract, and 1 cup vegetable oil in a blender until smooth, about 2 minutes. Scrape into bowl with dry ingredients and whisk until just combined (some small lumps are okay).

   Step 5

   Scrape half of the batter into prepared baking pan and spread into an even layer with an offset spatula. Sprinkle reserved spice mixture over. Scrape remaining batter on top and carefully spread to edges of pan. Scatter chilled streusel over and gently press to adhere.

   Step 6

   Bake cake, rotating pan halfway through, until a tester inserted into the center comes out with a few moist crumbs attached, 40–50 minutes. Transfer pan to a wire rack and let cake cool in pan 15 minutes. Turn cake out onto rack; peel away parchment and discard. Let cake cool completely.

   Step 7

   Carefully place cake, streusel side up, on a large plate to serve.

   Do ahead: Cake can be baked 2 days ahead. Store, loosely covered, at room temperature.