Preheat your oven to 350F and spray a 9x5 loaf pan with baking spray. Line the bottom of the pan with a strip of parchment paper.
Remove the plastic wrap from the bowl. Zest and juice half an orange into the soaked fruit, then zest half a lemon into the fruit. Add the brown sugar and mix all ingredients together until comined.
In a large bowl, whisk together the flour and pumpkin pie spice. Pour the fruit mixture into the dry ingredients and stir with a wooden spoon or spatula to combine. The dough will be lumpy and thick.
Stir the beaten egg into the dough until completely combined.
Transfer the Bara Brith dough into the prepared loaf pan, pressing down lightly so the dough is spread in an even, thick layer.
Bake Bara Birth for 60-70 minutes, or until a toothpick inserted into the center comes out clean.
Remove Bara Brith from the oven and let cool in the pan for 15-20 minutes. Run a knife around the edges of the pan, then invert bread onto a cooling rack. Carefully remove the parchment paper, then turn Bara Brith rightside up and let finish cooling on the wire rack.
You can serve Bara Brith at room temperature, but I prefer it when it's still slightly warm.