Preheat the oven to 350℉. Spray a 9×5-inch loaf pan with nonstick spray.: You will notice the oven warming and a faint heat that feels steady when you open the door. Preheating ensures the loaf begins rising immediately, creating a tender crumb rather than a dense center. If the oven is not fully heated, the bread can bake unevenly, so use an oven thermometer for accuracy. When greasing the pan, coat every corner so the loaf slips out cleanly; if it sticks, let it cool slightly before attempting to remove.
In a small bowl, stir together the cinnamon-pecan ingredients. Set aside.: The aroma of toasted pecans and cinnamon will bloom as you mix, and you may catch a toasty, sweet perfume. Combining these elements ahead of time ensures even distribution in the loaf and prevents the nuts from sinking. One mistake is adding them directly to the batter without mixing first, which can cause uneven pockets of spice. Keep the mixture dry and free of clumps by breaking any larger nut pieces.
In a large bowl, stir together the flour, sugar, baking powder and salt. In a medium bowl, beat the egg with a fork, and then stir in the milk and oil. Add the egg mixture to the flour mixture. Stir just until moistened (it will be lumpy).: As you whisk the dry ingredients, you will see the pale, even tone that signals uniform leavening. When you mix the wet ingredients, the egg will coat the milk and oil , creating a glossy, cohesive liquid. Folding the wet into the dry just until moistened preserves tenderness; overmixing develops gluten, making the loaf chewy. Watch for small streaks of flour disappearing into the batter as the sign to stop. A common error is vigorous mixing, which leads to a dense loaf, so use gentle strokes.
Spoon half of the batter into the prepared pan. Sprinkle with half of the cinnamon-pecan mixture. Pour the rest of the batter on top. And then sprinkle the rest of the cinnamon-pecan mixture on the very top. Use a butter knife to cut down through the batter and pull up and around to create a swirled, marbled effect.: When you spoon the batter in, you will hear a soft plop as it lands. The layered approach creates defined ribbons of spice and nut. As you swirl with the knife, move with a light touch so the colors merge without completely blending, creating the marbled look. If you press too hard you will eliminate the swirl, and if you do it too little the layers may remain unintegrated. Aim for sweeping, shallow cuts that rise and fall like gentle waves.
Bake for 55 to 60 minutes (or until a wooden pick inserted into the center comes out clean). Cool in a pan on a wire rack for 10 minutes. Remove the bread from the pan, and let it cool completely on a wire rack. Wrap and store overnight before slicing.: During the bake you will hear soft crackles as the crust forms and smell the intensified cinnamon and toasted pecans . The top should turn a warm golden brown, and the center will spring back slightly when touched. The wooden pick test is key because baking times vary by oven; if the pick comes out with wet batter, return the loaf for additional minutes. Cooling on a rack prevents sogginess from trapped steam. If you slice too soon, the crumb may be gummy, so patience yields cleaner slices. Wrapping overnight melds flavors, but avoid airtight wrapping while still warm to prevent condensation.