Cook the barley: Put the pearl barley, 3 cups water, and 1 teaspoon of the kosher salt into a medium saucepan. Bring it to a boil over high heat.

Stir the barley once when the water boils. Cover the saucepan and reduce the heat to low.

Cook the barley for 28 to 32 minutes, until the grains are tender but still a little chewy in the center.

Check the saucepan. If there is more than a spoonful of water left, pour the barley into a colander to drain it.

Return the barley to the saucepan. Drizzle in 1 teaspoon of the olive oil, cover the pan, and set it off the heat to keep warm.

Start the bean mixture: Warm the remaining 2 tablespoons olive oil in a large skillet over medium heat.

Add the chopped onion and red bell pepper to the skillet. Stir so the vegetables are coated with the oil.

Cook the onion and pepper for 7 to 8 minutes, stirring every minute or two, until the onion is soft and the pepper looks glossy with a few browned edges.

Add the tomato paste and smoked paprika to the skillet. Stir for 1 minute, until the tomato paste darkens a little and smells sweet instead of raw.

Add the drained butter beans, 1/2 cup water, the remaining 1/2 teaspoon kosher salt, and the black pepper to the skillet.

Stir gently so you do not break up the beans too much. Let the mixture simmer for 3 to 4 minutes, until the beans are hot and the sauce lightly coats them.

Add the baby spinach to the skillet in two batches. Stir after each batch until the leaves collapse and turn dark green.