Sweet Potato Crisps with a Creamy Chilli Sauce

I’ve based the flavourings in this dipping sauce on yuzo kosho, the tongue-tingling Japanese citrus paste made from pounding green chillies with salt and yuzu skin. Brushed on grilled meats or spooned into ramen or hot pots, its spicy floral taste is an epiphany. You can buy jars from Asian stores, but I’ve riffed a homemade version using lime zest and jalapeño, swirled here into a creamy buttermilk base.