Preheat oven to 350°F (175°C). Grease and line an 8-inch (20cm) square or round baking pan.
Place chopped dates in a bowl, pour over boiling water, add baking soda, and let sit for 10 minutes to soften.
In a medium bowl, whisk together flour, baking powder, cinnamon, nutmeg, and salt. Set aside.
In a large bowl, cream the butter and brown sugar until light and fluffy. Beat in eggs one at a time, then stir in vanilla extract.
Fold the softened date mixture into the batter.
Gradually add the dry ingredients, alternating with milk, mixing just until combined.
Gently fold in the diced apple.
Pour batter into the prepared pan and smooth the surface. Bake for 35–40 minutes, or until a skewer inserted into the center comes out clean.
For the citrus syrup, combine sugar, orange juice, lemon juice, and zest in a small saucepan. Stir over medium heat until sugar dissolves, then simmer for 3–4 minutes. Stir in butter until melted.
Poke holes all over the warm pudding with a skewer.
Slowly spoon hot citrus syrup over the top, allowing it to soak in. Cool slightly before serving.
