In a large mixing bowl, whisk together the egg, egg yolk, Greek yogurt, sourdough discard, white sugar, brown sugar, vanilla, pumpkin purée, and oil until smooth.

In a medium bowl, whisk together flour, cinnamon, ginger, nutmeg, cardamom, baking soda, baking powder, and salt.

Add dry ingredients to wet. Beat wet ingredients with a whisk or a hand mixer until everything is well combined. Do not overmix.

Overnight Fermentation: Cover tightly with plastic wrap and refrigerate for 8–12 hours for added fermentation benefits. If baking same day, skip this step.

If you fermented batter overnight, remove from the refrigerator and allow to come to room temperature for an hour to soften the batter.

Make the cinnamon sugar ripple. Add the flour, white sugar, brown sugar, cinnamon, ginger, nutmeg, and salt. Combine together well and set aside for later.

In another small bowl, melt butter needed for the crumble. Add the flour, white sugar, brown sugar, cinnamon, ginger. and nutmeg to the melted butter. Using a spoon or your fingers, combine ingredients until butter has been incorporated and you have a crumbly mixture. Set aside for later.

Preheat oven to 425°F. Line a 12-cup muffin pan with parchment liners, and gently spray with cooking spray to avoid sticking.

If batter was fermented overnight, gently mix with a spatula to combine ingredients.

In each muffin cup, spoon 1 ½- 2 Tablespoons of batter into the bottom until all 12 have batter at the bottom. Use a toothpick of you need to make sure batter covers the bottom of the muffin cups.

Sprinkle a spoonful of the cinnamon sugar ripple over the tops of all of the muffins.

Scoop roughly 2 Tablespoons more of the batter on top of the cinnamon ripple. Use a toothpick or skewer if needed to spread the batter to the edge of the muffin pan.

Top each muffin with 1 Tablespoon of crumble, and gently press down with your fingers to help crumble stick to the muffin tops.

Place the muffins in the oven and bake at 400°F for 6 minutes, then without opening the oven, reduce the temperature to 350°F (175°C) and bake for another 18-20 minutes, until the tops are golden and a toothpick inserted in the center comes out clean.

Let muffins cool in the pan for 5 minutes, then transfer to a wire rack to finish cooling.

Sift powdered sugar into a mixing bowl. Add maple syrup and 1 Tablespoon of milk. Using a whisk, combine ingredients. If glaze is too thick, add 1 teaspoon of milk at a time until glaze is thick but pourable.

Drizzle fresh glaze over the tops of cooled muffins. Allow the glaze to rest 15 minutes to set before serving.

Enjoy your Sourdough Pumpkin Coffee Cake Muffins!