• Preheat the oven to 400 degrees F. Line a 12-count muffin pan.

Make the Streusel Topping

• In a small bowl, whisk together the sugar, flour, cinnamon, and salt.
• Mix in the melted butter. Set aside.

Make the Cinnamon Sugar Mixture

• In a small bowl, whisk together the brown sugar, cinnamon, and salt.
• Mix in the melted butter. Set aside.

Make the muffins

• In a medium bowl, whisk together the flour, cinnamon, baking powder, baking soda, and salt.
• In a large mixing bowl, using an electric mixer, cream together the softened butter and brown sugar until well combined.
• Add the milk, oil, eggs, and vanilla extract to the creamed butter and sugar and mix until well combined.

  Note: at this stage, the butter will seize a bit making the mixture lumpy. Don't worry, the muffins will turn out perfectly!
• Add the dry ingredients to the wet ingredients and mix until combined.
• Scoop the batter into the lined muffin tin filling each one about 1/3 full.
• Evenly distribute the cinnamon sugar mixture into each well.
• Top with the rest of the batter until each well is about 3/4 full.
• Using a toothpick or knife, give each muffin a quick swirl to help the layers come together.
• Evenly distribute the streusel on top of each muffin pressing down gently to help it stick.
• Bake for 18 to 20 minutes or until golden brown and a toothpick inserted in the center comes out clean.
• Allow the muffins to cool in the pan for 5 minutes then transfer them to a wire rack to cool for another 20 minutes before serving.