Sift the flour (200g), cinnamon (2 teaspoons), and baking powder (1 teaspoon) in a medium bowl. Mix to incorporate.
In a large bowl, whisk together the light brown sugar (200g), egg (1) and egg yolk (1) until smooth
Drizzle in the oil (120ml) and vanilla extract (1 teaspoon) and whisk to combine.
Fold in the shredded carrots (200g). Set the mixture aside for 10-15 minutes.
Fold in the flour mixture, and mix just until the flour is hydrated. Refrigerate for 1-2 hours. Make the streusel while you wait.
Preheat oven to 350F. Line a muffin pan with muffin liners.
Divide the batter between the muffin liner, 3/4 full (for 12 muffins), or all the way full (for 9 muffins).
Top each muffin with the streusel.
Bake for 20-24 minutes turning the pan halfway the baking time.
Streusel
In a medium bowl, place the flour (90g), cinnamon (1 teaspoon), chopped nuts (120g), and sugar (70g) and use a fork to incorporate.
Drizzle in the melted butter (70g) and use the fork (or your fingers to blend ingredients together). Set aside while making the muffins.
Notes
All of the ingredients must be at room temperature before starting to mix.
For added flavor, consider adding, orange zest from one orange, a handful of golden raisins or shredded coconut to the muffin batter. And during fall, you can replace some or all of the carrots with pumpkin puree for delicious pumpkin muffins.
If you prefer a healthier option, you can substitute half of the all-purpose flour with white whole wheat flour.
Be sure not to overmix the batter, which can result in dense and tough muffins. Mix just until the dry ingredients have been incorporated.