
This moist banana bread is tender, warmly spiced, and packed with ripe banana flavor. Sour cream, melted butter, and a little oil keep the loaf soft for days, making it perfect for breakfast, snacks, or afternoon tea.
Preheat the oven to 350°F / 180°C, or 320°F / 160°C for a fan oven. Position a rack in the center of the oven.
Line a 8.5 x 4.5-inch / 21.5 x 11.5 cm loaf pan with parchment paper, leaving some overhang on the long sides so the loaf is easy to lift out.
In a medium bowl, whisk together the flour, baking soda, salt, cinnamon, and allspice until evenly combined.
In a large bowl, mash the bananas until mostly smooth. Measure out 1 3/4 cups mashed banana and reserve any extra for another use.
Add the brown sugar, eggs, egg yolk, sour cream, melted butter, vegetable oil, and vanilla extract to the mashed banana. Whisk until the mixture is smooth and well blended.
Add the dry ingredients to the banana mixture. Fold gently with a spatula just until no dry streaks remain; a few small lumps are fine.
Pour the batter into the prepared loaf pan and smooth the top.
Bake for about 70 minutes, rotating the pan halfway through, until the top is deeply golden and a skewer inserted into the center comes out clean or with only a few moist crumbs.
Let the banana bread cool in the pan for 10 minutes. Lift it out using the parchment paper and transfer to a wire rack.
Cool for at least 1 hour before slicing so the crumb sets properly. Serve plain, lightly warmed, or spread with butter.
Use very ripe bananas with lots of brown spots for the best flavor. Do not overmix once the flour is added, or the loaf can turn dense. Store tightly wrapped at room temperature for up to 3 days, refrigerate for up to 1 week, or freeze slices for up to 3 months.