Preheat your oven to 300°F (150°C). Prepare the cake pan by lining it with parchment paper.
In a large mixing bowl, whisk together butter and sugar until the mixture is pale and fluffy.
Gradually add eggs, beating well after each addition, then mix in the vanilla extract and orange zest.
In another bowl, whisk together flour, baking powder, salt, and mixed spice.
Gradually mix dry ingredients into the creamed mixture alternately with orange juice.
Gently fold the dried fruits and nuts into the mixture until they are thoroughly incorporated.
Pour the batter into the prepared cake pan and smooth the top with a spatula.
Bake for about 2 to 2.5 hours or until a toothpick inserted into the center comes out clean.
After baking, let the cake rest in the pan for 10 minutes before transferring it to a wire rack to cool completely.