In a medium mixing bowl, combine brown sugar, all purpose flour, and cinnamon. Whisk together and add the melted butter. Mix until crumbles form and place into the freezer.
Add room temperature cream cheese to a large bowl. Using an electric hand mixer, mix on medium speed for about 20-30 seconds, until smooth and fluffy. Then add powdered sugar, vanilla extract, egg yolk, and a pinch of salt. Continue to mix until smooth and combined, about 1 minute. Set aside.
In a large mixing bowl, combine flour, baking soda, baking powder, salt, cinnamon, nutmeg, ginger, allspice, and cardamom. Whisk together and set aside.
In a separate bowl, whisk together brown sugar, sugar, vegetable oil, and sour cream. Whisk until smooth, then add eggs and vanilla extract, and canned pumpkin puree. Continue to whisk together until smooth and all ingredients are fully incorporated.
Add the dry ingredients to the wet ingredients and whisk until just combined and there are no patches of flour, about 20 seconds. Do not overmix.
Line two muffin pans with muffin/cupcake liners in every other muffin cup. Pour batter to the top of each lined muffin cup (about ¼ cup of batter). Dollop 1 tbsp of the cream cheese mixture on top of the muffin, then add the cinnamon streusel on top of the cream cheese.
Pour 3 tbsp of water into the empty muffin cups.
Bake one pan at a time for 5 minutes at 425 degrees. Then reduce the heat to 350 degrees and baking for 14-17 minutes, until a toothpick inserted into the center of the muffin comes out clean.
Notes
We're baking 6 muffins at a time using a 12-cup muffin pan. That means there's 6 empty muffin cups. There's a small trick here - add about 3 tbsp of water to the empty muffin cups. This creates steam while the muffins are baking in the oven and keeps your muffins nice and moist. It also prevents your pan from warping. It's a win win all around.
Don't Overmix the Batter: Mix the wet and dry ingredients until just combined to avoid tough muffins. Overmixing can lead to dense, chewy muffins instead of soft and fluffy ones.
Check for Doneness with a Toothpick: Insert a toothpick into the center of a muffin; if it comes out clean or with just a few crumbs, they’re done. This helps prevent overbaking, which can dry out the muffins.
Let Them Cool Properly: Allow the muffins to cool in the pan for about 10 minutes before transferring them to a wire rack. This prevents them from becoming soggy and helps them keep their shape.