Preheat the oven to 180°C/355°F. Grease a large glass or ceramic ovenproof dish (I used a 9 Inch or 23cm square baking dish). *note 6
Place the sugar, eggs, and apricot jam in a large mixing bowl or the bowl of a stand mixer, and beat (with a whisk attachment) until the mixture is light and fluffy (this takes about 3-5 minutes). This can be done by hand.
1 cup white granulated sugar, 2 eggs, 2 tablespoons apricot jam
Sieve the flour, baking soda, and salt into the egg mixture. Mix until just combined. The batter with be thick.
1½ cups plain flour, 1½ teaspoons baking soda, ½ teaspoons table salt
Either in a small saucepan, or a microwave-proof bowl or jug, heat together the milk, butter, and vinegar, mixing until combined. The mixture will curdle. This is fine.
2 tablespoons butter, ½ cup milk, 2 tablespoons vinegar
Add the butter mixture to the batter and whisk until a smooth batter forms. Scrape down the sides of the bowl and make sure everything is well combined.
Pour the malva pudding batter into the glass or ceramic dish, and smooth to the edges. Cover the dish with an ovenproof lid or with tin/aluminum foil. Bake in a preheated oven for 20 minutes. Then remove the lid or foil cover, and bake for a further 15-20 minutes or until the malva cake is a deep golden brown and a cake tester/toothpick comes out mostly clean from the center of the pudding. *Note 7
During the last 10 minutes of the sponge baking, combine all the sauce ingredients in a saucepan. Stir the ingredients together on medium-high heat until the butter is completely melted, the sugar is dissolved, and the sweet sauce is heated all the way through.
380 mL evaporated milk, ⅓ cup light brown sugar, ½ cup butter, ½ cup water, ½ teaspoons table salt
Once the sponge is baked, remove it from the oven. Prick all over the pudding with a cake tester, skewer, or toothpick. Pour the sauce over the top of the pudding. At first, it will look as if there is too much sauce, but it will be rapidly absorbed into the sponge.
Serve the warm pudding with some fresh cream, custard, or a scoop of ice cream.