To make the crumb topping, whisk flour, sugar, and salt in a medium bowl. Stir in nuts. Add butter; using your fingertips, work butter into dry ingredients until large, moist crumbs begin to form. Refrigerate topping until ready to use.

Preheat oven to 350°. Coat a 9-inch springform pan with nonstick spray.

To make the cake, in a medium bowl, whisk flour, cornmeal, baking powder, baking soda, and salt; set aside.

Using an electric mixer on medium speed, beat 3/4 cup sugar and butter in a medium bowl until light and fluffy, 3–4 minutes. Beat in vanilla. Add eggs one at a time, beating to blend between additions and occasionally scraping down sides of bowl, until mixture is pale and fluffy, 3–4 minutes longer.

With mixer on low speed, add dry ingredients to bowl in 3 additions, alternating with buttermilk in 2 additions, beginning and ending with dry ingredients. Pour half of batter into prepared pan and smooth top. Whisk remaining 3 Tbsp. sugar and cinnamon in a small bowl; sprinkle evenly over batter in pan. Spoon remaining batter over; smooth top.

To make the pumpkin filling, in a small bowl, whisk together the light brown sugar, salt, cinnamon, and nutmeg. Add the egg and egg yolk and whisk until evenly combined. Stir in the heavy cream. Add the pumpkin puree and whisk until smooth. Pour the pumpkin filling over the coffee cake and gently spread evenly over the top.

Sprinkle crumb topping over pumpkin filling.

Bake cake until top is golden brown and a tester inserted into the center comes out clean, 55–60 minutes. Let cool completely in pan.

Store in airtight container at room temperature. (This is a great make-ahead cake. I think it tastes even better the day after being baked.)