For streusel: In a medium saucepan, melt butter over medium heat. Cook until butter turns a medium-brown color and has a nutty aroma, about 10 minutes. Remove from heat, and let cool to room temperature.
In a medium bowl, whisk together flour, pepitas, sugars, and salt. Drizzle with browned butter; stir with a wooden spoon until combined. Crumble with your fingertips until desired consistency is reached.
Preheat oven to 350°F (180°C). Spray a 9-inch springform pan with baking spray with flour. Line pan with parchment paper.
For cake: In the bowl of a stand mixer fitted with the paddle attachment, beat butter and sugars at medium-high speed until combined, 5 to 7 minutes, stopping to scrape sides of bowl. Reduce mixer speed to low; add eggs, one at a time, beating well after each addition. Add pumpkin, beating just until combined.
In a medium bowl, whisk together flour, salt, cinnamon, nutmeg, baking soda, baking powder, and ginger. With mixer on low speed, gradually add flour mixture to butter mixture alternately with milk, beginning and ending with flour mixture, beating just until combined after each addition. Pour batter into prepared pan, smoothing top with an offset spatula. Sprinkle with streusel.
Bake until a wooden pick inserted in center comes out clean, 55 minutes to 1 hour. Let cool in pan for 10 minutes. Run a sharp knife around edge of cake to loosen sides. Remove from pan, and let cool completely on a wire rack.
Notes
Using an entire 15 oz. can of pumpkin makes for a very moist, almost pumpkin-pie like cake. For a less decadent texture and tender crumb, use 1 cup (244 grams) of pumpkin instead of a 15 oz. canned pumpkin.
Recipe by Bake from Scratch at https://bakefromscratch.com/pumpkin-cake-with-brown-butter-streusel/