In a medium bowl sift together flour, baking soda, and salt. Set it aside.
Using a mixer fitted with the paddle attachment, beat together butter and sugar until fluffy, 3-4 minutes. Add 1/3 cup maple syrup and beat for one more minute. Scrape down the sides and the bottom of the bowl as needed. On medium speed, beat in the eggs one at a time, beating well after each addition. Add mashed bananas and vanilla extract and beat until well combined. With the mixer on low speed, add half of the dry ingredients and beat just until combined. Add the yogurt or sour cream and beat until combined. Add the other half of the dry ingredients and beat just until combined. Do not overmix – the less you mix, the lighter the bread will be. Mix in the nuts, reserving a few for garnish.
Pour batter into prepared loaf pan and top with reserved nuts. Bake for 50-60 minutes until a toothpick inserted into the center of the bread comes out clean. If the top is browning too quickly, cover the pan loosely with aluminum foil (I cover mine after 30 minutes to help prevent it). Remove from oven and place the pan on a wire rack.
Warm the maple syrup in a small saucepan over low heat until heated through (or for a few seconds in the microwave). Drizzle slowly over banana bread while the bread is still warm. If the syrup doesn’t soak in completely, poke a few holes with a toothpick. Allow the bread to cool completely in the pan.
Store bread at room temperature in an airtight container for up to 2 days or refrigerate for up to 5 days. Serve at room temperature. The bread can be frozen for up to 2 months. Thaw it on the counter, still covered, or overnight in the fridge.