This sauce was born from my love for treacle toffee. The sweet, dark, rich potency of treacle has always made me think of it as a savoury condiment rather than a sweet ingredient. The spices in this sauce confirm its grown-up savoury role.
Heat the vegetable oil in a large saucepan over a medium heat. When hot, add the black mustard seeds and fry for about 30 seconds until they pop and turn grey.
Next add the rest of the ingredients and stir well until everything is fully combined. Cook over a low heat for 15–20 minutes, stirring regularly, until the sauce has reduced and thickened. Add a splash of water to loosen the mixture up a little if it’s too thick.