Preheat the oven to 350 degrees F. Spray 4 mini loaf pans with cooking spray. Set aside.: As the oven warms to 350 degrees F , you will notice a dry, warming scent that promises browning. Preheating ensures the batter begins rising immediately once it goes in, producing a tender interior and nicely colored crust. When you spray the pans, the oil sheen helps the loaves release cleanly after baking, so you wont tear the crumb. A common mistake is putting the pans in a cold oven, which leads to dense centers and underdeveloped rise. Also, if your oven runs hot, consider using an oven thermometer so the true temperature matches the number you dialed.
In a medium bowl, whisk together flour, baking soda, salt, cinnamon, and nutmeg. Set aside.: When you whisk these dry elements, you are creating homogeneity; the baking soda and spices disperse so every forkful has even flavor and lift. The aroma of ground cinnamon and nutmeg will become more pronounced as you whisk, a pleasant sign that the spices are active. This distribution prevents clumps of leavening which can cause uneven rise and bitter pockets. Avoid adding wet ingredients to the dry mix before it is fully combined, which can create streaks or pockets that will not incorporate properly.
In a large bowl, whisk together sugar, oil, water, pumpkin, eggs, and extracts. Whisk until smooth and combined.: As you whisk the wet ingredients, observe how the batter turns satin and glossy, with the pumpkin blending into the liquid to create a thick, orange hue. The eggs and oil emulsify to bind fats and water, ensuring the final crumb is tender and not crumbly. This stage is also when the vanilla and hazelnut notes bloom, adding aromatic complexity. If lumps of pumpkin remain, gently press them against the bowl with the whisk to smooth them out. Avoid vigorous whipping which can incorporate excess air and change the crumb structure.
Slowly stir in the flour mixture. Mix until ingredients are combined.: As you fold the dry mix into the wet, watch the batter thicken and the color deepen to a rich, spiced orange. Gentle stirring prevents overdevelopment of gluten, which keeps the loaf tender; the feel should be thick and slightly ribboning as it falls from the spoon. If you see streaks of dry flour, continue folding carefully until just combined. Overmixing here will tighten the crumb and yield a tougher loaf, so stop as soon as the flour disappears. If the batter looks too stiff, a splash of water can rescue it, but measure cautiously.
Pour the batter into the mini loaf pans, making sure batter is evenly divided. Drop 2 heaping tablespoons of Nutella onto each loaf pan. Swirl the Nutella into the pumpkin batter with a knife. Place the loaf pans onto a baking sheet and place in the oven. Bake for 40-45 minutes or until a toothpick comes out clean.: As you portion the batter, note the glossy surface and even distribution of spices. Dropping Nutella by spoonfuls creates concentrated pockets that will melt into ribbons as the loaf bakes, offering pockets of gooey, hazelnut chocolate. When you swirl, move the knife just enough to create marbling, do not over swirl or the contrast will blend away. During baking, the kitchen will fill with a caramelized, toasty scent and the tops will develop a gentle crust. Check doneness with a clean toothpick inserted near a Nutella pocket, you want the stick to come out mostly clean with a few moist crumbs, not wet batter. A mistake to avoid is opening the oven too often while baking, which can lower the temperature and cause uneven rise.
Place the loaf pans on a wire rack. Cool for 15 minutes in the pan and then carefully remove the loaves. Cool completely before slicing.: The immediate post bake period is crucial; you will notice steam rising from the pans as the loaves rest, and the crumb continues to set. Cooling for 15 minutes allows the interior to stabilize so the loaves will release cleanly from the pans. When you remove them, the surface should spring back slightly to the touch, and smells of toasted hazelnut and spice will be strong. Allowing the loaves to cool completely prevents the Nutella from running out when you slice, producing clean marbled slices. Cutting too soon is a common error that leads to crumbly slices and melted filling spilling out.
Note - You can make regular size loaves. This recipe should make 2 8 x 4 loaves. Adjust baking time to about 60 minutes.: Scaling up to full size loaves yields deeper centers and more substantial slices, and the aroma in the oven intensifies as the larger mass browns. For 8 x 4 pans, bake until a toothpick comes out clean and the top is a deep golden brown, which typically takes about 60 minutes. The longer bake time allows the center to cook without burning the crust, and rotating the pans halfway through can promote even coloring. A pitfall is crowding the oven, which reduces air circulation and lengthens bake time unpredictably, so leave room around each pan.