Add the flour, baking powder and shortening to a bowl. Mix using a fork and breaking up the shortening incorporating into the flour until you see small balls. Stir in the sugar and currants or raisins, lemon zest and milk. Mix until you get a soft, sticky dough. Do not over mix.

Grease a 1-quart (4 cup) heatproof bowl with the shortening.

Add the dough to the bowl and cover with parchment paper and foil. Crimping the edges of the foil around the edge to seal, leaving room at the top in case the pudding expands.

Place a cookie cutter or something similar in the bottom of the pan so the bowl is not sitting directly on the bottom of the pan.

Place the bowl, foil side up on the cookie cutter into the pan and fill 2/3 up the bowl with hot water. Cover the pan with a lid, bring to a boil and simmer for 2 hours. Check periodically to make sure the water doesn’t boil dry.

While the pudding steams, make the custard.

Stir together the milk and sugar over medium heat and bring to a simmer.

While the milk is coming to a simmer, add the eggs to a mixing bowl and whisk in the cornstarch until smooth.

Slowly whisk 1/3 cup of the hot milk into the egg mixture until smooth. This will temper the eggs and stop them from curdling or cooking.

Pour the egg and milk mix back into the pan with the milk and whisk over low heat until thickened.

Once the custard has thickened, remove from the heat.

Stir in the vanilla and mix until well incorporated.

When the pudding is ready, carefully lift out of pan and remove foil. Use a knife to carefully loosen the pudding around the edge. Turn out onto a cooling rack to cool slightly.

Slice into wedges and serve with hot custard.