Set a large nonstick skillet over medium heat and a small saucepan over medium-low heat.

Put the sour cream into a small bowl. Stir in the lime zest and 1 tablespoon of the lime juice, then set the bowl aside for serving.

Pour 1 tablespoon of the olive oil into the saucepan. Add half of the scallion whites and cook for 1 minute, stirring, until they start to soften.

Add the black beans to the saucepan with 1/2 teaspoon of the cumin, the chili powder, 1/4 teaspoon of the salt, and 1/3 cup water. Stir, bring the beans to a gentle simmer, then lower the heat so they stay warm while you make the fritters.

Put 1 cup of the corn into a medium bowl. Mash it well with a fork until many of the kernels are broken and the mixture looks a little pasty; this helps the fritters hold together.

Add the remaining corn, the chopped roasted red peppers, the remaining scallion whites, and half of the scallion greens to the bowl with the mashed corn.

Crack the eggs into the bowl. Stir until the eggs coat the corn and peppers evenly.

Add the flour, baking powder, the remaining 1 teaspoon cumin, the remaining 1/2 teaspoon salt, and the black pepper to the bowl. Stir just until a thick batter forms.

Pour 1 tablespoon of the olive oil into the large skillet and let it heat until it looks loose and shiny.

Scoop the batter into the skillet in 1/4-cup mounds, making 4 fritters. Press each mound gently with the back of a measuring cup or spoon so each fritter is about 1/2 inch thick.

Cook the fritters for 3 to 4 minutes, until the bottoms are deep golden brown and the edges look set.

Turn the fritters with a thin spatula. Cook for 3 minutes more, until the second side is browned and the centers feel firm. Transfer the fritters to a plate.