Most cooks know what mirepoix, soffritto, and the Holy Trinity are...but kroueng? That's a little less likely. The answer is that it's a variety of aromatic flavor pastes used in Khmer cooking, such is in these delicious beef skewers that I learned from my Chinese-Cambodian mother-in-law. Here, I did my best to recreate the original flavor of her recipe using more readily available ingredients. The good news: She approves.