Line a muffin tin with paper cups. Preheat the oven (top/bottom heat: about 180°C, hot air: about 160°C).
Put flour, brown sugar, baking powder and baking soda in a mixing bowl and mix. Grate the orange zest over the top. Place egg, oil and buttermilk in a measuring cup and whisk to combine.
Pour onto the flour mixture and knead with hand mixer (dough hook).
Stir in the poppy seed cake. Rinse the blueberries and pat dry with kitchen paper.
Carefully fold them into the dough. Pour the batter into the prepared muffin tins and bake for about 25 minutes. The muffins can also be prepared with fresh cranberries.