Prepare the fresh ingredients: Roughly chop the garlic and red chilies if your blender is not very powerful.
Blend: Combine the garlic, red chilies, mayonnaise, plain Greek style yogurt, harissa chili paste, ground cayenne, sumac, crushed red pepper flakes, freshly squeezed lemon juice, and kosher salt in a high-speed blender. Cover and blend until smooth. (You may need to uncover and push down the ingredients with a spoon 1-2 times in between if your blender is not very powerful.) Taste and adjust spices, salt, and stir in more lemon juice if needed.
Serve: Use immediately or transfer to a sealed airtight container and store in the fridge until ready to use. Enjoy with spicy meat stuffed pitas, kofta rice bowls, kebabs, shish rolls, salads, sandwiches, burgers, taco and use as a spread, dip, or dressing.
Storing: Store in a sealed airtight container/jar in the refrigerator and consume within 5-7 days.
Harissa Chili Paste: This is a spicy and smoky Tunisian chili pepper paste. It’s made with roasted red peppers, dried chilies, and other spices and herbs. It is available in squeezable tubes, cans, and small jars. I recommend DEA or Le Phare Cap Du Bon harissa as they are the most authentic. Their harissa is also spicier than most brands. Other brands may also add tomato powder or paste to the harissa and will be sweeter in flavor. Look for it in Middle Eastern/Mediterranean grocery stores, the Middle Eastern or international aisle of a well-stocked supermarket, or order it online.
Adjust spice level to taste. Feel free to add more or less of the fresh red chiles, ground cayenne, and crushed red pepper flakes depending on your heat level preference. You can use less harissa too if you wish. Note that harissa comes in varying heat levels depending on the brand. Use less if you’re sensitive to heat and if you know the particular brand of harissa you’re using is on the spicier side.