Preheat oven to 190°C/375°F; place three large oven trays in the oven while preheating.
Remove and discard kale stems from leaves. Wash leaves well; pat dry with paper towel or in a salad spinner. Tear kale leaves into 5cm (2-inch) pieces; place in a large bowl, then drizzle with oil and sprinkle with salt. Using your hands, rub oil and salt through the kale. Spread kale, in a single layer, on trays.
Bake kale for 10 minutes. Remove any pieces of kale that are already crisp. Return remaining kale to the oven for a further 2 minutes; remove any pieces that are crisp. Repeat until all the kale is crisp. Cool.
These kale chips will keep in an airtight container for up to 2 weeks.