01 -
Peel your onion and garlic, then roughly chop them up. Toss everything into a blender and blend until you get a smooth mixture. Strain this through a muslin cloth or fine mesh strainer to extract just the juice, then pour it into your cooking pot.
02 -
Heat up your pan and add the onion-garlic juice along with ¾ cup water, sugar, salt, both vinegars, black pepper, and nigella seeds if you're using them. Bring this beautiful mixture to a rolling boil, stirring until all that sugar completely dissolves.
03 -
In a small bowl, whisk together the remaining ¼ cup water with the cornstarch until you have a smooth, lump-free slurry. This is your secret weapon for getting that perfect sauce consistency.
04 -
Pour your cornstarch slurry into the simmering sauce and keep stirring continuously over medium heat. Watch as it transforms into a glossy, thick sauce that coats your spoon beautifully - this usually takes just a few minutes.
05 -
Remove the pot from heat and stir in that fresh lemon juice for a bright finish. Let the sauce cool completely to room temperature, then transfer to an airtight container and refrigerate until you're ready to enjoy it.