Preheat oven to 350°F (180°C). Spray a 13x9-inch baking pan with cooking spray. Line pan with parchment paper, letting excess extend over sides of pan.

In a large bowl, whisk together squash, granulated sugar, oil, ⅓ cup (76 grams) melted butter, ¼ cup (55 grams) brown sugar, eggs, and 1 teaspoon (4 grams) vanilla.

In a medium bowl, whisk together 2¾ cups (344 grams) flour, baking powder, 1¾ teaspoons (5.25 grams) salt, cinnamon, baking soda, allspice, nutmeg, cloves, and pepper. Gradually stir flour mixture into squash mixture just until combined. Spoon batter into prepared pan, smoothing into an even layer with a small offset spatula. Tap pan on a kitchen towel-lined counter a few times to settle batter and release any air bubbles.

Bake until top and center of cake are mostly set and an instant-read thermometer inserted in center registers about 185°F (85°C), 23 to 26 minutes.

Meanwhile, in another medium bowl, stir together cream, remaining 1 cup (220 grams) brown sugar, remaining ⅓ cup (76 grams) melted butter, remaining 2 teaspoons (6 grams) flour, remaining ½ teaspoon (1.5 grams) salt, and remaining ½ teaspoon (2 grams) vanilla. Stir in pecans. Spoon and spread mixture onto hot cake.

Bake until cream mixture is bubbly, a wooden pick inserted in center comes out with just a few moist crumbs, and an instant-read thermometer inserted in center registers 200°F (93°C), 6 to 8 minutes. Let cool completely in pan on a wire rack.

Using excess parchment as handles, remove cooled cake from pan, and cut into squares as desired.