Preheat the oven to 200C /400F. Lightly grease a heavy bottom Dutch-oven or a high-sided oven-proof dish with a lid. Sprinkle the base of the pan with flour and set aside.
In a large mixing bowl, combine the flour, salt, bicarbonate of soda, and seeds.
Make a well in the center of the flour mix and pour half the buttermilk into the well and gradually stir to combine. Pour in the remaining buttermilk and stir to bring together into a dough.
On a floured surface, turn out the dough and form it into a flattened ball to resemble a similar width to your ovenproof dish.
Transfer the dough to your Dutch oven and using a sharp knife cut across the dough vertically and horizontally to form a cross.
Put into the oven and bake for 30 minutes, then cook for a further 10 minutes with the lid on.
Once cooked, carefully remove from the oven and leave for 10 minutes to cool before carefully turning out the bread onto a wire rack. Enjoy warm or leave to completely cool.