Start by preheating your oven to 325°F (160°C). Line an 8-inch round cake pan with parchment paper and grease it lightly to prevent sticking.
Beat the softened butter and sugar in a large bowl until the mixture is light and fluffy. This step is key to achieving a soft and tender cake texture.
Crack the eggs into the bowl one at a time, beating well after each addition. This will keep the batter smooth and evenly mixed.
In another bowl, sift together the flour, baking powder, salt, and pumpkin pie spice. Mix well to ensure the spices are evenly distributed.
Gradually add the dry ingredients to the creamed mixture, alternating with the milk. Stir gently until the batter is smooth and all ingredients are combined.
Toss the currants, raisins, and golden raisins with a small amount of flour to coat them. This helps prevent the fruit from sinking during baking. Carefully fold them into the batter.
Pour the batter into the prepared tin, smoothing the surface with a spatula. This ensures an even bake.
Place the tin in the preheated oven and bake for 1½–2 hours. Check the cake by inserting a skewer into the center; it should come out clean. If the top begins to darken too quickly, cover it with a sheet of foil.
Remove the cake from the oven and let it cool in the tin for about 20 minutes. Then transfer it to a wire rack to cool completely. Once cooled, slice and enjoy!