Grease a 9"x5" loaf pan. Line with parchment paper. Grease the paper. Set aside.
Preheat oven to 425 degrees F.
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, 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. Make a slice down the middle with a knife (the batter will be sticky).
Place in the hot oven and bake for 10 minutes. Turn the temperature down to 375 degrees F (do not remove the breaand bake for additional 30 to 35 minutes, or until a toothpick inserted in the center comes out clean and the top is golden brown.