Heat the olive oil in your large pot over medium heat, then add the onions, carrots, and potatoes. Cook for about 8 minutes, stirring occasionally, until the onions turn translucent and the potatoes begin to soften slightly.
Stir in the minced garlic and let it cook for just one more minute. Garlic burns fast, so keep an eye on it and stir constantly during this short step.
Add the chopped chicken, corn, frozen spinach, chicken broth, and milk straight into the pot. Give everything a good stir so it's evenly distributed before moving on to the next step.
Sprinkle in the white cheddar powder along with the black pepper, whisking continuously as you add it. Whisking here prevents any clumping and helps the broth turn silky and smooth.
Let the soup simmer gently for 5 to 10 minutes, stirring occasionally, until the broth thickens up and the potatoes are fully cooked through. Once it looks creamy and the potatoes are tender, it's ready to serve.