Preparation Steps

• Heat oven to 350°F (175°C). Line a 9×5-inch loaf pan with parchment leaving a bit overhang, then lightly grease the paper and sides.
• In a large bowl whisk the egg with both sugars until combined and slightly pale. Whisk in the warm coconut oil, sour cream, and vanilla until smooth, then fold in the mashed banana.
• In a separate bowl stir together the flour, baking powder, baking soda, salt, and cinnamon. Break up any lumps so the leaveners are evenly distributed.
• Add the dry mixture to the wet in two additions, folding gently with a spatula until just incorporated. The batter should be thick but scoopable; avoid overmixing to keep the loaf tender.
• Fold in the grated zucchini (press it in a clean towel or paper towel if very watery) and the optional walnuts or chips. If the batter still seems thin, sprinkle in 1–2 tablespoons extra flour to reach a slightly thick consistency.
• Spoon the batter into the prepared pan and smooth the top. Let the filled pan rest at room temperature for 5–10 minutes while the oven finishes preheating — this helps air bubbles redistribute for a more even rise.
• Bake on the middle rack for 50–65 minutes. Check at 45 minutes; if the edges and top are browning too quickly, tent loosely with foil. The loaf is done when a toothpick in the center comes out clean or with a few moist crumbs.
• Remove from oven and cool in the pan on a wire rack for about 15–20 minutes. Use the parchment overhang to lift the loaf from the pan and cool completely before slicing (about another 30–60 minutes) for cleaner slices.
• Store wrapped at room temperature for 2 days or refrigerate up to 5 days. For longer storage, freeze sliced and wrapped for up to 3 months.