Preheat the oven to 350°F (175°C) and line a loaf pan with parchment paper.

In a bowl, mix the all-purpose flour, brown sugar, granulated sugar, salt, nutmeg, baking soda, and ground cinnamon.

Add the oil and mix until incorporated.

Continue mixing until the mixture forms coarse crumbs.

In a separate bowl, whisk the egg until smooth.

Add half of the crumb mixture and the buttermilk to the beaten egg.

Mix until a smooth batter forms.

Transfer the batter to the prepared loaf pan and spread it evenly.

Sprinkle the remaining crumb mixture evenly over the top.

Bake for 45–55 minutes, or until a toothpick inserted into the center comes out clean.

Remove from the oven and allow the loaf to cool in the pan for about 10 minutes, then transfer it to a wire rack to cool completely.