Preheat your oven to 180 degrees Celsius, and line your tin with baking parchment.
In your mixing bowl, mix together the self-raising flour, baking powder, salt, and caster sugar.
Now, rub the butter into the flour mixture using your fingertips. You're looking for a crumbly texture, a bit like breadcrumbs.
Next, crack your egg into a separate bowl, add the buttermilk and give it a good whisk. We're adding air here, folks!
Gradually add your wet ingredients to your dry ones, mixing as you go. Then, fold in the mixed seeds if you went for this option.
Once your dough comes together (it'll be quite sticky, don't panic!), spoon it into your lined tin. Use a spatula or the back of a spoon to smooth the top.
Pop your tin into the preheated oven and bake for about 60 minutes. You're looking for a lovely golden brown crust and a skewer inserted into the middle should come out clean.
Once baked, let your loaf cool in the tin for about 15 minutes, then remove it and let it cool completely on a wire rack.
When your loaf is completely cool, cut it into rusks (thick slices first, then each slice into fingers). Arrange these on a baking tray and dry them out in a very low oven (about 70 degrees Celsius) for 8 hours or overnight.
