Start by bringing a large pot of salted water to a boil. Once boiling, add the elbow pasta. Cook it until it's al dente, which usually takes about 7-8 minutes. You don’t want it too soft; it will bake further in the oven. Drain the pasta and set it aside.

In a medium saucepan over medium heat, melt the butter. Add the minced onion and cook until it becomes translucent, about 3 minutes. This aroma? It’s the magic beginning. Sprinkle in the flour and whisk vigorously for about 2 minutes—this is your roux, which will lend creaminess to the sauce.

Gradually stir in the skim milk and broth, maintaining the whisking rhythm. Bring this mixture to a gentle boil and let it thicken, which should take about 5 minutes. Next, remove the pan from heat and stir in the shredded cheddar cheese until melted. Season with salt, pepper, and the smoked paprika.

Once your cheese sauce is smooth and creamy, toss in the baby spinach. It’s better when the spinach wilts slightly. Watch it transform before your eyes, becoming vibrant green and tender.

In a large bowl, mix the drained pasta with the cheese sauce. Make sure every bit is coated beautifully. This step is crucial as it ensures each bite is equally delicious.

Preheat your oven to 350°F (175°C). Transfer the macaroni mixture into a baking dish. Sprinkle the seasoned breadcrumbs evenly on top. Lightly spray with olive oil to encourage crispiness. Bake for about 25 minutes, until the top is golden brown and bubbly.

After removing the dish from the oven, let it sit for about 5 minutes. This step allows the sauce to settle just enough to avoid a soupy mess when you serve.