To make your base muffin batter, whisk together the flour, sugar, baking powder, baking soda, and salt in a bowl

In a separate bowl, whisk eggs, melted butter, milk, sour cream, and vanilla until smooth

Pour wet ingredients into the dry ingredients and whisk gently until just combined — don’t overmix! The batter will be thick with a few small lumps

Divide the batter evenly into 4 bowls (about 1 cup of batter per bowl). Each bowl will make three muffins

For the pumpkin muffins, in one bowl, add the pumpkin puree, spices, and flour, folding in until just combined

For the apple muffins, in a new bowl, toss the diced apples with the cinnamon and flour to coat, before folding into one of the prepared bowls of base batter

For the chocolate chip muffins, fold in the chocolate chips and flour just until combined

For the raspberry white chocolate muffins, toss the raspberries in a bowl with the flour to coat, then fold into the remaining bowl of base batter along with the white chocolate chips

Cover all four bowls and place in the fridge for at least an hour. This will thicken the batter to help provide structure for those domed muffin tops

While the batter is in the fridge, make your oat streusel by combining the flour, oats, brown sugar, cinnamon, and salt in a bowl. Then stir in the melted butter until you have a crumbly mixture. Place in the fridge to firm up the butter

Preheat oven to 425°F and line every other cup of a 12-cup muffin tin with muffin liners. Bake 6 muffins at a time, for maximum heat distribution, to help with the final puff

Remove your pumpkin muffin and raspberry white chocolate muffin batter from the fridge

Split each of your batters between the six muffin liners - 3 per flavor. Top your pumpkin batter with half of your oat streusel and top your raspberry muffin batter with 1-2 extra raspberry halves and 2-3 white chocolate chips

Bake for 5 minutes, then without opening the oven, drop the temperature to 350°F and bake for an additional 15-18 minutes until a toothpick inserted comes out with just a few moist crumbs. Let the muffins cool in the pan for 5 minutes before transferring to a wire rack to cool completely

Return your oven to 425°F and re-line your muffin pan, every other cup for a total of 6 muffin liners

Divide your chocolate chip muffin batter and apple muffin batter between the liners. Then press some extra chocolate into the tops of the chocolate muffin batter and the remaining streusel on top of the apple batter

Place in the oven and bake for 5 minutes, drop the temperature to 350°F, and bake for an additional 15-18 minutes. Let the muffins cool in the pan for 5 minutes, then transfer to a wire rack to cool completely