If using sour milk: place 1 tablespoon of white vinegar in a measuring cup and fill with enough milk to make 1 and ½ c. Stir few times and let sit for 2 to 3 minutes.
In a large mixing bowl, whisk together the dry ingredients (flour, sugar, baking soda and baking powder). Add orange zest and whisk.
In a medium mixing bowl, beat eggs. Add buttermilk, oil and vanilla and mix well.
Add wet ingredients to dry ingredients and stir with a wooden spoon or rubber spatula just until moistened. Do NOT overmix the batter!
Pour half the batter into prepared pan and spread evenly. Drizzle the apricot preserves and gently make few swirls in the batter. Top with remaining batter and spread evenly.
Bake for 35 to 40 minutes or until a toothpick inserted in the center of the bread comes out clean.