This spicy curry sauce can be found all over Britain—in chip shops and pubs, and even bottled (or powdered) in markets to use as a simple sauce to turn leftover roast dinners into a simple meal the following day. The spice can be tailored to the level of heat you want, but the aromatics and toasted spices make a fantastic base for any number of dishes.
What you end up with at the end of this recipe is an intense, thick curry sauce that can be kept in the fridge for up to a week (or a few months in the freezer). Once you've made this base curry you can add it to chopped up leftovers from a roast dinner, then add stock or water.
This amount of base curry is enough to make a leftover dinner for 4 people if you add 1 cup of additional liquid along with your leftovers. Or alternately, make up a big batch of salty French fries and pour this sauce over for a heaping batch of curry fries.
Depending on how you're going to serve it you can either choose to puree the sauce, or not. To me, the non-pureed thicker sauce if preferable for a meal sized curry that you're going to simmer with other ingredients (roast lamb or chicken, and leftover vegetables), but if I'm making curry fries and using it more as a dipping sauce then I would take the extra step of pureeing and straining it.