Scoop the 3½ cups of buckwheat groats into a large bowl or pot and cover with water by about 4 cms. Put a plate or lid on top and leave at room temperature overnight or at least 6 hours. Soak the sunflower and pumpkin seeds in a separate dish, adding half a teaspoon of salt and enough water to cover the seeds by a few centimetres.
After soaking, strain the groats using a sieve or colander, and rinse lightly. Return the groats to the bowl and add the salt and 1 cup of water. Use a whizz stick to puree the groats so you get a smooth batter. Strain and rinse the seeds, and then stir them through the batter.
Cover the bowl with a plate and leave out at room temperature for 24 hours. If it's particularly cold you might need to leave it for a few hours' longer, but you will know that your bread batter is ready when it's formed a slight dome from rising. In hot weather it will ferment faster and you might find it's ready in half the time.
Preheat your oven to 200˚C. Pour the batter into a silicone loaf pan (I sit my silicone pan inside a glass one so that it keeps its shape when it is full). Sprinkle sesame seeds on top.
Turn the oven down to 180˚C. Cook the bread for 1 hour 15 minutes until it is golden brown and crusty. Gently tip the bread out of the loaf pan and leave on a rack to cool for at least 30 minutes before slicing and eating!
As with all fermenting, I recommend avoiding metal dishes or utensils. I personally use a large ceramic bowl and a wooden spoon. I bake the bread in a silicone loaf pan because the greased glass loaf pan experiment was an epic fail - the bread stuck to the sides in a major way! I had to chisel it out with a knife... You could also use baking paper to line your loaf pan of course.