Preheat the oven to 350 degrees. Grease a loaf pan and cover the bottom with a piece of wax paper (or parchment paper) to fit the bottom and grease the paper.
If using a stand mixer, attach the paddle. You can alternatively use a hand-held mixer.
Into the mixer bowl add the flour, baking powder, baking soda, cinnamon, nutmeg, cardamom, sugars, salt, butter, and oil. Combine the ingredients on low for 2 minutes.
In another mixing bowl combine the bananas, eggs, vanilla and buttermilk.
On low speed, scrape the banana mixture into the flour and blend ingredients on low for about 30 seconds.
Pull the bowl from stand mixer and gently fold the batter with a silicone spatula to finish combining.
Scrape the batter into the greased loaf pan. Evenly sprinkle the streusel topping over the top.
Bake for one hour and 10 minutes. If your oven runs hot, begin checking for doneness around 1 hour.
Insert a toothpick into the middle of the banana bread. If there is “gooey” batter on the toothpick, place back in the oven for another 5 minutes. Check again with a clean toothpick.
Be careful not to overbake. Everyone’s oven heats and bakes differently. You are looking for a toothpick with just a few crumbs stuck to it. Continue to bake as needed so that your toothpick has those few crumbs.
Remove from the oven and allow to cool for 20 minutes.
Run a sharp knife around the edges of the pan, or if you’re concerned about scratching your pan, you can use a very thin silicone or plastic spatula to slide around the edges to loosen the bread.
Tilt the loaf pan slightly with one hand and help maneuver the bread out of the pan with your other hand and onto a platter, streusel side up.
If you can resist, allow the bread to cool for 30 minutes, only for the convenience of the slices not falling apart. We still ate the very warm bread with forks because we had no patience.
Serve at room temperature or still slightly warm.
Store leftovers in an airtight container for up to 3 days.