1 cup chopped walnuts
1 cup all-purpose flour
1/2 cup white sugar
1/4 cup lightly packed brown sugar
1 1/2 teaspoons baking powder
1 teaspoon ground cinnamon
1/2 teaspoon salt
1 large egg, at room temperature
1/2 cup whole milk, plus more as needed
2 tablespoons oil
2 teaspoons vanilla extract
Preheat the oven to 350 degrees F (180 degrees C). Spray an 8 1/2 x 4 1/2-inch loaf pan with non-stick cooking spray; set aside. Spread walnuts onto a baking sheet.
Toast walnuts in the preheated oven until nuts start to turn golden brown and become fragrant, about 10 minutes. Set aside to cool.
Whisk flour, sugar, brown sugar, baking powder, cinnamon, and salt together in a bowl; set aside.
Crack and stir egg in a measuring cup. Add milk to the 3/4 cup measuring line. Add oil and vanilla; stir until well combined. Pour into flour mixture; stir just until all ingredients are moistened. Pour batter into the prepared pan.
Bake in the preheated oven until a toothpick inserted in the center comes out clean, 35 to 45 minutes. Cool on a wire rack for 15 minutes before removing from pan to cool completely.