Preheat the oven to 425 degrees F. Wash and dry sweet potatoes, then place onto a baking sheet. Bake in the oven for 35-45 minutes, until they become fork tender and begin to slightly leak a brownish color syrup (this means the sweet potatoes have caramelized - yum!)
Reduce the oven temperature to 325 degrees F. Line a 9x5 inch loaf pan with parchment paper so that there's about 2 inches overhang. Set aside.
Remove the skin from the sweet potatoes and place into a large mixing bowl. Use an electric hand mixer to mix the sweet potatoes until mashed and smooth. Set aside to cool for at least 20-30 minutes, until just warm but not hot.
Add brown sugar, sugar, melted butter, and vegetable oil. Use an electric hand mixer to mix everything together for about 2-3 minutes, until combined and smooth.
Add eggs, sour cream, and vanilla extract. Mix to combine, then add the dry ingredients - all purpose flour, spices, baking soda, and kosher salt. Continue to mix until fully combined, about 15-20 seconds.
Make sure streusel by combining brown sugar, cinnamon, flour, and a pinch fo salt. Add melted butter and use a fork to mix together until the texture resembles crumbly wet sand.
Pour the batter into the prepared loaf pan and top with the streusel. Bake for 1 hour and 20-30 minutes. Allow the bread to cool in the pan for 10 minutes, then remove onto a wire rack to cool completely.
Notes
Prep the sweet potatoes correctly! Roast, Don’t Boil: Roasting sweet potatoes enhances their natural sweetness and keeps them from getting waterlogged, which can negatively impact the bread’s texture. Also, allow the sweet potatoes to cool prior to assembling the batter.
Measure Accurately - Use a kitchen scale: Weighing your mashed sweet potatoes ensures consistent results. Sweet potatoes can vary in moisture, so a consistent weight keeps the recipe balanced.
Don’t Skip Draining: If the sweet potato mash seems wet, drain it using a fine mesh strainer or cheesecloth to avoid excess moisture.
Toothpick Test: Insert a toothpick in the center; it should come out with a few moist crumbs but not wet batter.