Spicy Tex-Mex Black Bean Enchiladas

In a medium microwave-safe bowl, whisk together half the cornstarch (all for 4 servings), half the Tex-Mex paste, and 1/2 cup hot water (1 cup for 4) until smooth. Cover with a paper towel and microwave 1 minute. Uncover; whisk mixture until smooth. Cover and microwave until thickened, 30 seconds more. Whisk again until smooth. (If your sauce is still too watery—it should be the consistency of gravy, not water—you may need to continue microwaving and whisking in 30-second intervals.)

Heat a drizzle of oil in a large pan over medium-high heat. Add green pepper and cook, stirring occasionally, until beginning to soften, 4-5 minutes. Add scallion whites and garlic; cook, stirring, until fragrant, 1 minute more. Add tomato, Southwest Spice Blend, and remaining Tex-Mex paste; stir to coat. Add black beans and their liquid and 1 tsp salt (2 tsp for 4 servings); stir to combine. Cook, stirring occasionally, until beans are saucy and liquid has reduced, 3-4 minutes.

Place a small amount of filling on one half of each tortilla. Roll up tortillas, starting with filled sides, to create enchiladas. Place, seam sides down, in an 8-by-8-inch baking dish (use a 9-by-13-inch baking dish for 4 servings).

Pour Tex-Mex sauce over enchiladas to thoroughly coat. Sprinkle with cheese. Bake on top rack until sauce is bubbling and cheese melts, 3-5 minutes.