Preheat and Prep – Preheat your oven to 350°F (175°C). Grease and line a standard loaf pan with parchment paper for easy removal.
Make the Orange Purée – Place the whole orange or mandarins in a food processor and blend until completely smooth.
Mix Wet Ingredients – In a large mixing bowl, whisk together the eggs, sugar, oil, and vanilla extract. Stir in the orange purée and Greek yogurt (or sour cream) until well combined.
Incorporate Dry Ingredients – In a separate bowl, whisk together the flour, baking soda, and salt. Gradually fold the dry ingredients into the wet mixture, stirring just until combined.
Bake – Pour the batter into the prepared loaf pan. Bake for 50–60 minutes, or until a toothpick inserted in the center comes out clean. If the top browns too quickly, tent it with foil halfway through baking.
Cool Slightly – Let the cake cool in the pan for 10–15 minutes before transferring it to a wire rack.
Make the Glaze – While the cake cools, whisk together the melted butter, milk, powdered sugar and zest until smooth.
Glaze and Enjoy – Pour the glaze over the warm cake, allowing it to soak in slightly. Sprinkle with extra orange zest for a pop of color and extra citrus aroma. Slice and enjoy!