Preheat your oven to 350°F (175°C). Line a muffin tin with paper liners or grease it lightly.
In a small bowl, mix together the flour, brown sugar, and cinnamon. Add the softened butter and mix until crumbly. Set aside.
In a large bowl, whisk together the flour, granulated sugar, brown sugar, baking powder, baking soda, salt, and ground cinnamon until well combined.
In another bowl, whisk together the melted butter, eggs, brewed coffee, and vanilla extract until fully incorporated.
Pour the wet ingredients into the dry ingredients. Gently stir with a spatula until just combined. Be careful not to overmix; some lumps are okay. Fold in the nuts if using.
Divide the batter evenly among the prepared muffin cups, filling each about ¾ full. Sprinkle a generous amount of the crumb topping over each muffin.
Bake in the preheated oven for 18-22 minutes, or until a toothpick inserted into the center comes out clean. The tops should be golden brown.
Once baked, remove the muffins from the oven and allow them to cool in the pan for 5 minutes before transferring them to a wire rack to cool completely.
Notes
Serve warm or at room temperature, dusted with powdered sugar.