Preheat the oven to 375°F. Weigh or measure your dry ingredients, then sift them all and mix in a medium-sized bowl.
In a liquid measuring cup, add and measure vegetable oil then add eggs, vanilla and sour cream. Mix until blended.
Prepare the carrots. Use a box grated or food processor, to finely grate the carrots.
Add and mix the grated carrots and sugar to the dry ingredients, then add the egg mixture. Mix just until incorporated. Do not overmix.
Add the toasted chopped walnuts and fold in the cake batter mixture just until combined.
Use an ice cream scoop or measuring cup to divide the cake batter and fill the 12-muffin pan lined with parchment. Fill about 3/4 full each muffin cup.
Bake in a preheated oven to 375°F for 10 minutes, then reduce the temperature to 350°F. Continue baking for another 8 to 10 more minutes or until the inserted toothpick comes out clean.
Remove from the oven and let it cool in the muffin pan for 10 minutes, then remove from the pan to cool completely.