Preheat your oven to 375°F (190°C) and line a 12-cup muffin tin with paper liners or grease thoroughly. Pro tip: Spraying the top of the muffin pan helps prevent any overflow from sticking, making cleanup significantly easier.
In a medium bowl, whisk together the flour, pumpkin pie spice, baking powder, baking soda, salt, and espresso powder. The coffee granules should be evenly distributed throughout the dry mixture.
In a large bowl, whisk the pumpkin puree, granulated sugar, and brown sugar until well combined. Add the oil, eggs, milk, and vanilla extract, mixing until you achieve a smooth, consistent batter.
Gradually fold the dry ingredients into the wet mixture, stirring just until combined. Stop mixing as soon as no dry flour pockets remain to avoid overmixing.
In a small bowl, combine the flour, brown sugar, cinnamon, and pumpkin pie spice for the streusel. Using your fingertips or a pastry cutter, work the cold butter into the mixture until it resembles coarse crumbs. Mix in the chopped pecans if using.
Divide the batter evenly among the prepared muffin cups, filling each about ¾ full. Sprinkle the streusel topping generously over each muffin, gently pressing it into the batter slightly.
Bake in the preheated oven for 22-25 minutes, or until a toothpick inserted in the center comes out clean with just a few moist crumbs. Rotate the pan halfway through baking if your oven has hot spots.
Allow the muffins to cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.
While cooling, prepare the coffee glaze by whisking together the powdered sugar, cooled coffee, and vanilla extract until smooth. Adjust consistency as needed by adding more coffee or powdered sugar.
Once the muffins have cooled for at least 10 minutes, drizzle the coffee glaze over the tops using a spoon or piping bag.