For the red bean paste:
200g (1 cup) dried red beans, rinsed and picked over
100g (½ cup) sugar
90g (½ cup) canola oil
For the salted egg yolks:
2 cups coarse salt
6 large raw egg yolks
For the dough:
300g (2 ½ cups) all-purpose flour, plus more for dusting
110g (½ cup) canola or other neutral-flavored oil
160g (½ cup) golden syrup (like Lyle’s Golden Cane Syrup)
8g (1 teaspoon) alkaline water
For the filling:
250g (¾ cup) red bean paste
6 salted large egg yolks, cut in half
For the egg wash:
1 large egg
2 tablespoons water
For the red bean paste:
In a large bowl, cover the beans with 4 inches of water and let soak for at least 8 hours or overnight. Drain and rinse the beans.
In a medium saucepan, combine the beans and enough water to cover by 2 inches. Bring the water to a simmer and continue to cook until the beans are tender, 40 to 50 minutes. Drain the beans and rinse under cold water.
Transfer the beans to the bowl of a food processor and add the sugar. Puree until smooth.
Transfer the paste to a medium nonstick skillet. Add 1/4 cup of the oil and cook over medium-low heat, stirring with a flexible spatula until blended and smooth. Add the remaining 1/4 cup oil and cook, stirring, until the paste is darker in color and the oil is completely blended in, 8 to 10 minutes. Transfer paste to a heat-proof container and set aside to cool completely. Refrigerate until ready to use. Paste can be refrigerated in an airtight container for up to 2 weeks or frozen for up to 3 months.
For the salted egg yolks:
Pour half of the salt into a medium container with a tight-fitting lid. Gently place the egg yolks on the salt, spacing at least 1/2 inch apart. Cover the egg yolks with the remaining salt and cover with the lid. Refrigerate the egg yolks for at least 3 days or up to 5 days.
Preheat the oven to 200°F. Remove the yolks from the salt and rinse under cold water. Pat each yolk dry with a paper towel. Set dry yolks on a wire rack set over a large rimmed baking sheet and bake until dried and firm, 90 minutes.
Allow the yolks to cool and then refrigerate in a small airtight container until ready to use (up to 1 month).
For the dough:
In a large mixing bowl, combine flour, canola oil, golden syrup, and alkaline water. Using a flexible spatula, mix to form a shaggy dough, then knead with your hands to form a smooth, cohesive dough. Form the dough into a thick disc, wrap in plastic, and allow it to rest at room temperature for 45 minutes. Meanwhile, preheat the oven to 350 degrees and line a large rimmed baking sheet with parchment paper.
To assemble and bake the mooncakes:
On a lightly dusted work surface, divide the dough into 12 equal portions with a bench scraper (for accuracy, weigh with a digital scale, if you have one). Roll each piece into a smooth ball. Working with one piece of dough at a time, flatten with your palm and roll out dough into a 4 inch round. Continue to lightly dust with flour if sticking. Use a bench scraper to help lift up the dough.
Fill with 1/2 tablespoon bean paste, then half a salted egg yolk, and top with another 1/2 tablespoon paste. Bring the edges of the dough up around the filling. The dough won’t initially cover all of the filling; just pinch it together until it completely wraps the filling. Pinch together any cracks that form and roll into a smooth ball.
Arrange the balls on the prepared baking sheet, spacing at least 2 inches apart. Lightly dust the mooncake mold with flour. Press the plunger of the mold down to apply pressure, but take care not to press too hard. Gently release from the mold. Repeat with remaining dough and filling to form more mooncakes.
Bake mooncakes until the edges are lightly golden brown, 9 to 11 minutes. Remove the sheet from the oven and allow the cakes to cool on the sheet for 10 minutes.
Make the egg wash:
In a small bowl, mix together egg and water. With a pastry brush, lightly coat the mooncakes with egg wash. Return to the oven and bake until deep golden brown, 10 minutes. Transfer the baking sheet to a wire rack and allow the mooncakes to completely cool on the sheet. Store mooncakes in an airtight container at room temperature for 1 to 2 days to allow the dough to soften before serving.