For the batter: Combine 1 ¾ cups gluten free flour blend (or AP flour if not gluten free), 1 ¼ tsp. baking powder, ¼ tsp. baking soda, and a pinch of kosher salt in a mixing bowl. Stir to combine.
Add 1 stick of softened unsalted butter to a Kitchen Aid mixer and beat for a minute or so using the paddle attachment. Add ½ cup sugar and ½ cup packed dark (or light) brown sugar. Beat for 2-3 minutes until light and fluffy.
Add 1 Tbsp. vanilla extract and 2 large eggs. Beat for another 30 seconds or so.
Add the flour mixture and 1 heaping cup of pumpkin puree to the butter/sugar mixture alternately, starting and ending with the flour mixture. Add ⅓ of the flour mixture and beat. Add ½ of the pumpkin puree and beat. Continue until all of the flour and pumpkin is added. The batter should be light and fluffy.
For The Streusel:
Combine 1 ½ cup gluten free oats (or any brand if not gluten free), ½ cup gluten free flour blend (or AP flour if not gluten free), ¾ cup packed dark brown (or light brown) sugar, 2 ½ tsp. cinnamon, ¼ tsp. nutmeg, and a generous pinch of kosher salt to a bowl. Stir to combine. Drizzle 6 Tbsp. of melted unsalted butter into the mixture and stir to combine. The mixture should consist of large chunks.
Pour the batter into greased and floured pan and spread evenly. Add desired amount of the struesel topping on top of batter.
Place pan in oven and bake for 45 minutes or until toothpick comes out clean.
Remove pan from oven and cool completely before removing sides of springform pan.
Notes
Recipe adapted from Pretty Simple Sweet.Dark or light brown sugar can be used in this recipe.Use a round 9" cake pan if you do not have a springform pan.This pumpkin coffee cake is gluten free and uses a gluten free flour blend such as Bob's Red Mill 1 to 1 Flour or Cup 4 Cup. Gluten free flour blends work just as AP flour would and require no complicated substitutions or ingredients.Feel free to use AP flour if gluten is not an issue for you.Oats are naturally gluten free, but may be processed in a facility that also processes other products with gluten and cross-contamination can occur. Make sure to choose a brand of oats that are certified gluten free if gluten is an issue for you.