Preheat oven to 350 degrees. Line a 9 x 5-inch loaf pan with parchment paper, hanging over on two sides. Spray pan well with cooking spray.
Sauté spinach and garlic in olive oil for 2-3 minutes. Press between paper towels to remove any excess moisture.
In a medium bowl whisk together sour cream, vegetable oil and eggs. In a large bowl, whisk together remaining dry ingredients. Fold in spinach and stir until well incorporated. Add wet ingredients to dry and stir to combine.
Pour batter into prepared pan. Bake for 40 - 50 minutes until a toothpick in center comes out clean (ours went the 50 minutes). Drizzle top with melted butter.
Let cool 1 hour then remove loaf from pan and transfer to wire rack to cool completely.