It’s worth the time to roast bell peppers yourself. The flavor is deeper and the texture more velvety than roasted peppers from a jar.
Preheat the oven to 450°F.
Put a wire rack on a baking sheet and place the whole bell peppers on the rack. Roast the peppers, turning them now and then with tongs, until they blacken in spots, 30 to 40 minutes.
Transfer the roasted peppers to a large bowl and cover with plastic wrap. Let the peppers steam for 10 minutes. Uncover and let the peppers cool.
Remove the stems, skins, and seeds with a paring knife and cut the peppers into thin slices.