Begin by preheating your oven to 450°F and greasing an 11 x 8-inch ovenproof baking dish.
In a large bowl, combine 1⅓ cups (175g) all-purpose flour, 1 tbsp baking powder, ½ tsp salt, ¼ cup (55g) granulated sugar, ¼ cup (55g) softened salted butter, 1 extra-large egg, finely grated zest of 1 lemon, and ⅔ cup (150ml) milk.
Beat these ingredients together until the mixture reaches a soft, cake batter consistency. The batter should be smooth and pourable but still hold its shape when spread. This base will cook beneath the fruit and create the cake layer of the pudding.
Spread the batter evenly into your prepared baking dish, then arrange the drained apricot halves from 1 × 15-ounce (410g) can over the top, positioning them cut side down.
Brush or drizzle ¼ cup (55g) of melted salted butter over the apricots, ensuring even coverage. Sprinkle ¼ cup (55g) of demerara sugar generously over the buttered apricots. This topping is key—the larger crystals of demerara sugar will caramelize in the oven, creating the signature sticky, golden finish.
Bake for approximately 35 minutes, or until the top has caramelized to a deep golden brown. The pudding will continue to set slightly as it cools.
Serve the pudding warm for the best texture and flavor, accompanied by crème fraîche, whipped cream, or ice cream to complement the sticky-sweet apricots and tender cake base.