Wash and pat the flan mold or tin dry.
Prepare your steamer. Pour water into the base pot and set the steamer tray. Place a cloth on the steamer tray but make sure to not cover all the holes entirely.
Add sugar into the flan tin. Turn on the heat and let the sugar melt over low heat. Swirl the tin as the sugar start melting to distribute the heat. Avoid mixing with a spoon to prevent the sugar from crystalizing (see Note 1). Swirl the pan instead.
Cook until the sugar turns amber (see Note 2). Swirl the tin so that the caramel covers the entire bottom of the tin. Place the tin on a level surface and let the caramel set.
In a separate large bowl, whisk the egg yolks until smooth (with a hand whisk or a cake mixer) Do not overmix as it should not be incorporating any air bubbles.
Add the condensed milk, evaporated milk, salt and ube extract. Whisk again until all the ingredients are well combined.
Strain the custard with a fine mesh strainer onto the caramel layer in the prepared tin.
Use a large cloth to wrap the steamer pot lid. This will prevent water droplets from the steam that has accumulated on the lid from dropping into the leche flan (see Note 3).
Place the tin in the steamer and steam for 35 to 40 minutes on lowest heat. Check for doneness by inserting a toothpick in the center. If it comes out clean, the flan is cooked (see Note 4).
Remove the custard from the steamer and let it rest at room temperature until it cools down. Place the cooled custard in the refrigerator and chill overnight (see Note 5).
To serve, run a thin knife along the edges of the flan in the tin to create air pockets on the sides. Make sure it touches the bottom of the mold as you run it around. Place a rimmed plate on the tin , hold it tight to the tin and turn the tin over to transfer the ube leche flan onto the plate (see Note 6).
Lift the tin. Cut and serve the ube leche flan. The custard is best consumed chilled.
This recipe makes 450 ml custard.