200gcanned whole red beanspreferably Japanese red adzuki beans
Make tangzhong (roux):
In a small saucepan, whisk together bread flour and milk until no lumps remain. Set the saucepan over medium heat.
Cook gently, stirring continuously, until the mixture starts to thicken to a pudding-like consistency, about 3 to 5 minutes. Be careful not to overcook it! The roux is ready once the whisk/spatula leaves drag lines on the base of the pan, or when an instant-read thermometer reaches 65°C (149°F).
Scoop the roux into a small bowl. Cover with plastic wrap directly on the surface of the roux. Cool to room temperature (or cool in the chiller).
Make the main dough:
Grease the base and sides of 2 loaf tins measuring 20 x 10 x 10 cm (or similar sized loaf pans).
In a medium mixing bowl which can hold at least 2 cups of liquid, place the cooled tangzhong dough. Add the egg, water and whipping cream, and stir vigorously with a whisk until free of lumps and well incorporated.
In the mixer bowl of a stand mixer, combine bread flour, yeast, sugar and salt. Stir with a whisk to combine well. Pour in the tangzhong dough mixture. Start the mixer fitted with a dough hook, on low speed for one minute to allow the ingredients to come together.
Increase mixer speed to medium-high, and continue to knead until the dry and wet dough mixtures come together and form a rough dough. Knead until the dough cleans the sides of the bowl (referred to as pick up stage), about 3 to 5 minutes depending on the mixer speed.
Add the butter. Continue to knead until the butter is fully incorporated into the dough and the sides of the bowl come clean once more, and the dough is now smooth and elastic, about 5 to 7 minutes. Test for the 'windowpane' (see explanatory notes below).
Do the first proof (first rise):
Once 'windowpane' is achieved, turn out the dough onto the counter top and gather into a smooth ball. Lightly grease the base and up the sides of the same mixer bowl with some oil.Put the dough back in, rolling over once to grease the surface. Set aside, covered with a tea cloth, to proof for 40 minutes, or until the dough has doubled in volume.
Weigh the dough and divide equally into 4 portions. Round each dough portion into a ball and let rest for 10 minutes.
Do the second proof (final rise):
Roll out each ball into a long, flat rectangle about 5-mm (¼-inch) thick. Spread ¼ of the red bean filling over the surface of each dough. Roll it up like a Swiss roll.
Place two rolls of dough in each loaf pan. You can position the rolls with either the shorter end of the roll facing the short side of the pan, or facing the long side of the pan (see pictures above) - I've done it both ways.
Set aside to proof, covered with a tea cloth, for 50 minutes or until the dough has risen to ¾ of the height of the loaf tin.
Preheat the oven and bake:
When the dough is almost ready after the second proof, start preheating the oven until the temperature reaches 180°C (360°F). Bake for 30 to 35 minutes until the tops turn a deep golden brown and the loaves are baked through.
Remove the loaf tins from the oven. Brush the tops with melted butter (optional). Run a knife around the sides of each tin, and release the bread loaves immediately onto a cooling rack. Allow to cool completely to room temperature before slicing or storing.
The 'Windowpane Test' is done to check if the gluten in the dough is sufficiently developed. To do this, lightly grease your fingers and palms on both hands with some clean oil. Lop off a small portion of dough, roughly the size of a golf ball.
Gently tease and stretch the dough until you get a thin, continuous and translucent membrane (see photo above). You'll want to be able to get a stretch at least 5 to 6 cm (2 - 3 inches) wide.
If you get holes as you stretch the dough, it's okay so long as these tear in a circular fashion. If it tears too quickly or feels tight, it means the gluten isn't developed enough.
If this happens, stick the dough back with the rest in the mixer, and knead for another 2 to 3 minutes, before doing the test again. Keep repeating until you get the 'windowpane'.