1. Using a sharp paring knife, slice off the hard, central vein of each kale leaf.
2. Stacking 3 to 4 leaves at a time, cut them crosswise into half-inch strips.
3. Rinse in a colander or sieve and shake well, leaving some moisture clinging to leaves.
4. In a large Dutch oven or heavy pot, heat oil over medium-high heat.
5. Saute onion until translucent, about 4 minutes.
6. Add kale and mix until wilted, about 3 minutes.
7. Add tomatoes and garlic.
8. Cook, stirring, until tomatoes soften slightly, about 3 minutes.
9. Add beans and broth.
10. Bring to a boil, reduce heat and simmer until kale is tender, about 30 minutes.
11. Season to taste with salt and pepper.
12. Serve as a side dish or over brown rice for a main course.