These fluffy steamed buns are just like the ones you have your eye on when you go for Dim Sum.
The buns can be assembled up to 4 hours before steaming and kept refrigerated.
For the filling, place the beef in a small saucepan and add the ketchup, sugar, vinegar, soy sauce, hoisin sauce, ginger and 5-spice and stir occasionally over medium heat until the sauce reduces a little, about 5-7 minutes. Set aside to cool.
For the dough, sift the flours, sugar and baking powder into a large mixing bowl. Add the milk, water and oil and stir this with a wooden spoon until it becomes too difficult to do so. Turn the dough out onto a work surface and knead the dough by hand until it feels smooth and elastic, about 5 minutes. Set this back in the bowl, cover the bowl with plastic wrap and let the dough rest on the counter for an hour.
On a lightly flour work surface, cut the dough into 8 equal pieces. Roll each piece to as close to ¼-inch (6 mm) as possible, then using a 4-inch (10 cm) round cutter, cut out a circle. To fill each bun, hold a piece of dough in the palm of your hand and shape it with your fingers to make it more like a cup. Put a tablespoonful of the beef filling in the centre and then pinch the edges of the dough up and around to seal it in – it does take a bit of practice to make precise folds, so have patience. Place each bun, with the pinched end up, on a 2-inch (5 cm) square piece of parchment paper.
Fill the bottom of a wok or other large pot that will hold a large bamboo steamer with water and bring this to a full boil over high heat. Arrange 4 buns into the steamer (if you have 2 baskets, you can stack them, with 4 buns in each). Cover and steam for 13-15 minutes – the buns will open up as they steam – this is expected. Remove the steamed buns with tongs and serve within 40 minutes of steaming.