In a medium bowl, whisk the flour, brown sugar, cocoa powder, cinnamon, and salt together until combined. Add the butter and use a pastry cutter, two forks, or your fingers to blend until the mixture forms pea-sized crumbs. Stir in the mini chocolate chips. Cover and place in the refrigerator or freezer until needed in step 5.

Adjust the oven rack to the lower third position and preheat the oven to 350°F (177°C). Grease a metal 9×5-inch loaf pan with nonstick spray and line with parchment paper, leaving a couple inches of overhang on two opposite sides.* Set aside.

In a large bowl, whisk the flour, baking soda, pumpkin pie spice, cinnamon, and salt together until combined. Set aside. In a medium bowl, whisk the eggs, granulated sugar, and brown sugar together until combined. Whisk in the pumpkin, oil, milk, and vanilla. Pour the wet ingredients into the dry ingredients and whisk together until combined. The batter is thick and a few lumps are OK. Do not overmix. Transfer a heaping cup (about 280g) of the batter to a medium bowl; this will be the chocolate batter. Set aside the remaining pumpkin batter (the larger amount).

In a small bowl, combine the espresso powder and warm milk, whisking with a fork to dissolve the espresso powder. Pour this into the medium bowl with the smaller amount of batter, along with the cocoa powder, and whisk to combine. Fold in the mini chocolate chips.

Spread a thin layer of the pumpkin batter in the bottom of the prepared loaf pan. Layer a few spoonfuls of the chocolate batter on top, followed by a few spoonfuls of the pumpkin batter. Continue alternating spoonfuls of each batter until all of the batter is used. Gently shimmy the pan to level the batters. Using a knife, make rounded horizontal zigzags from one side of the pan to the other, followed by rounded vertical zigzags from top to bottom. Sprinkle the cold crumb topping evenly on top.

Bake for 60–70 minutes; loosely tent with aluminum foil around the halfway mark. The bread is done when a toothpick inserted in the center comes out clean with only a few small moist crumbs. This may be before or after 60–70 minutes depending on your oven, so begin checking every 5 minutes around the 55-minute mark.

Cool the bread completely in the pan set on a cooling rack. Lift the bread out of the pan by gripping the parchment paper overhang. Transfer it to a cutting board, then slice and serve.

Cover and store leftover chocolate marble pumpkin bread at room temperature for up to 3 days, or in the refrigerator for up to 1 week.