Prepare the Crumble: In a medium bowl, combine ¼ cup of room temperature salted butter, ⅓ cup of granulated sugar, and ½ cup of all-purpose flour. Use your fingers or a fork to mix until the mixture resembles sandy crumbs. Once ready, chill the crumble in the refrigerator while you prepare the muffin batter.

Make the Muffin Batter: In a large mixing bowl, whisk together ½ cup of melted salted butter, 1 cup of granulated sugar, 1 ½ teaspoons of vanilla extract, and ⅓ cup of vegetable oil until smooth and well combined. Next, add in 2 eggs and ⅓ cup of sour cream, whisking until fully integrated. Slowly mix in 3 cups of all-purpose flour, 1 tablespoon of baking powder, ½ teaspoon of baking soda, ¼ teaspoon of salt, and 1 cup of whole milk until just combined, being careful not to overmix. Gently fold in 1 ¼ cups of mini chocolate chips for a deliciously sweet surprise.

Rest the Batter: Cover the bowl with plastic wrap and let the muffin batter rest at room temperature for about 15-20 minutes while you preheat your oven to 425°F.

Prepare Muffin Tins: While the batter rests, line a 12-cup muffin tin with paper liners. Once the oven is preheated, carefully fill each muffin liner with the batter, filling them almost to the top for that delightful bakery-style look. Generously sprinkle the chilled crumble topping over each muffin.

Bake: Place the muffin tin in the preheated oven at 425°F. Bake for the first 5 minutes, then reduce the temperature to 350°F and continue baking for another 30-35 minutes.

Cool: Once baked, remove the muffin tin from the oven and allow the muffins to cool in the tin for about 15 minutes before transferring to a wire rack.