Prepare the Curry Paste: Prepare roasted peanuts by dry roasting them in a pan. Then pound the roasted peanuts into the pre-made panang curry paste until the paste is smooth again. If you don't have a mortar and pestle, you can blend the peanuts in blender and then stir them into the paste.
Partially Cook the Beef: Add ¼ cup of coconut milk to a pan and heat over medium heat. Add the thinly sliced beef1 and allow to cook until it is halfway done. Remove and set aside2.
Separate the Coconut Milk: Scoop the top ⅓ cup of thicker coconut milk from the can into a large pan or wok. Heat the coconut milk over medium heat until it is very bubbly and you start to see an oily sheen appear.3
Fry the Curry Paste: Add the prepared panang curry paste and stir into the separated coconut milk. Continue to cook until the aroma of the curry is strong. This usually takes about 5 minutes. Be sure to stir continuously and watch carefully so that the curry paste doesn't burn.
Make the Curry Sauce: Add the remainder of the coconut milk and water to the curry paste. Remove the central vein from the makrut lime leaves, tear in half, and add to the curry sauce. Allow to cook until the curry is your desired thickness, adding more water if necessary.
Season the Curry: Taste and adjust the seasonings with fish sauce and sugar as needed.4 Then add the thinly sliced red peppers, if using.
Add the Beef: When the curry is just how you like it, add the partially-cooked beef back in. Cook for another minute or so until it is just done, then remove from the heat.
Garnish and Serve: Spoon the curry into a serving bowl. Garnish with a sprinkling of chiffonade-cut makrut lime leaves.5 Serve with warm jasmine rice.
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Notes
To ensure tender beef, you need to start with a good cut of meat and slice it very thinly, against the grain. Naturally tender cuts of steak such as filet mignon, top sirloin, and strip steak are the best pieces to use. To make thin slicing easier, freeze the steak for at least 15 minutes, then use a sharp knife to cut it into slices about ⅛ inch thick.
This recipe relies on partially cooking the meat, then adding it back in after the panang curry sauce is done to make sure that it doesn't get overcooked and therefore tough. Instead of cooking it in coconut milk on the stovetop as presented here, you could alternatively pre-cook the beef in the Instant Pot. On the other hand, another option to ensure tender beef is to allow it to cook for a long time in the curry sauce. If you'd like to go this route, add the thinly-sliced beef after the curry paste has been fried in the coconut milk and is aromatic, then add the remainder of the coconut milk and water and allow to simmer for upwards of 30 minutes until the beef is nice and tender. You'll need to add more water as the beef cooks so the curry doesn't become too dry.
Some brands of coconut milk have emulsifiers added that make them less easy to separate into their milky and oily layers. You can add a teaspoon of mild-flavored oil to the pan if you aren't getting good separation.
Sugar and fish sauce are used to round out the curry. The amount of each of these will depend on which brand of curry paste you use, as some contain more salt and/or sugar than others. I typically use the Mae Anong brand of panang curry paste and add 1 teaspoon of sugar and 1 teaspoon of fish sauce to help round out the curry. You should taste and adjust accordingly.