Bring a large pot of water to a boil and add 1/4 teaspoon sea salt. Add the elbow macaroni and cook according to the package instructions until al dente. Drain the pasta well and set it aside for later use.

In a small bowl, combine the plain flour, remaining sea salt, and garlic powder (if using). Stir together to ensure the salt and garlic powder are evenly distributed throughout the flour.

In a medium saucepan over medium heat, melt the salted butter. Add the dry flour mixture from Step 2 and whisk continuously. Cook, stirring, for about 1 minute, until the mixture is slightly browned. This helps remove the raw flour taste and adds flavor.

Slowly pour in the whole milk, whisking constantly until the mixture is smooth and free of lumps. Add the sour cream or plain Greek yogurt and whisk until fully incorporated. Increase the heat to medium-high and cook until the sauce thickens, about 3 to 5 minutes. Make sure not to let the sauce boil. Once thickened, reduce the heat to low and gradually add the shredded cheddar cheese. Whisk until the cheese is completely melted and the sauce is silky smooth. Taste the sauce and feel free to add a little more salt or seasoning if you prefer—personally, I sometimes stir in a pinch of black pepper for an extra kick.

Add the drained, cooked macaroni from Step 1 to the saucepan with the cheese sauce. Stir everything together until the noodles are evenly coated in the luscious sauce. Let the mac and cheese sit for 3 to 5 minutes to help the sauce thicken slightly and cling to the noodles. Serve warm for the best, creamiest texture!