Line a large baking tin/tray (about 10.5"x15.5") with baking paper.
In a large bowl, stir together your oats, nuts, seeds, dark muscovado sugar, salt, cinnamon and mixed spice.
In a small saucepan over a medium heat, combine the butter, honey and golden caster sugar. Bring to a simmer, making sure to stir constantly with a whisk until the golden caster sugar has dissolved and the mixture has come together. Once fully combined, simmer for about 30 seconds then remove from the heat. Stir in the vanilla extract.
Pour the liquid mixture over the oat mixture in the bowl. Stir well until combined. Spread your granola onto your prepared baking tray and bake at 150°C until golden brown, this should take about 25-30 minutes. Once or twice during the baking time, take out, stir well and put back in for the remainder of the baking time.
Transfer your tray to a rack to cool. If using, add your dried fruit, mixed seeds or chocolate chips once the granola has cooled completely. If your granola has formed very large chunks, you can break these up if desired.
Store in an airtight container and enjoy.