Step 1

Preheat the oven to 350 degrees F.

Step 2

Cut the butter into small chunks.

Step 3

In a bowl, add 2/3 cup of the flour, 1/4 cup of the granulated sugar, 2 tablespoons of the brown sugar, the salt, and 1/2 teaspoon of the cinnamon and whisk to combine.

Step 4

Add the butter chunks to the flour mixture and mix with a wooden spoon or a spatula just until the dry ingredients get coated with the butter.

Step 5

Using your clean fingers, press the mixture into sand-like crumbs, with some larger ones remaining.

Step 6

Place the streusel in the refrigerator to chill.

Step 7

In a bowl, add the vegetable oil, 1/4 cup of the granulated sugar, and the remaining brown sugar and, using an electric hand mixer, whip together until pale and fluffy.

Step 8

Add the egg and whip until just combined.

Step 9

Into a bowl, sift the remaining flour, the remaining 1/4 teaspoon of the salt, and the baking powder together.

Step 10

Add the dry ingredients mixture into the oil mixture and fold to combine.

Step 11

In a small bowl, add the vinegar and the baking soda and mix to combine.

Step 12

Immediately fold the bubbly vinegar mixture into the batter.

Step 13

Spoon or pipe 1/2 of the batter into six cavities of a cupcake pan.

Step 14

In a bowl, add the remaining cinnamon and the remaining granulated sugar and mix to combine.

Step 15

Spoon the cinnamon-sugar over the batter in the cupcake tins evenly.

Step 16

Spoon or pipe the remaining batter over the top of the cinnamon sugar layer in the cupcake tins.

Step 17

Evenly and generously sprinkle the streusel mixture over the top of the muffin batter.

Step 18

Bake until a wooden skewer inserted into the center of the muffins comes out clean, about 25 minutes.

Step 19

Allow the muffins to cool on a cooling rack.

Step 20

Serve.