Meanwhile, add the cream, Dijon mustard, garlic powder, and cayenne to a small saucepan and whisk to combine.
Heat the cream mixture over medium heat. When the cream starts to bubble around the edges, lower the heat to low.
Stir in the shredded cheddar, ⅓ at a time, slowly and patiently with a rubber spatula until it is completely melted. Don't stir vigorously, or the sauce will become stringy. Turn the heat off as soon as it's all melted.
Pour the cheese sauce on the steamed broccoli and serve.
Video
Notes
Using store-bought pre-shredded cheese helps with the sauce's texture. The small amount of anti-caking agent typically added to shredded cheese (cornstarch or powdered cellulose) helps thicken the sauce.
If you're shredding your own cheese and feel that the sauce is too thin, stir in a bit more cheese - start with ¼ cup. You can also mix 1 teaspoon of cornstarch with 1 teaspoon of cold water and stir that into the sauce. This will add a tiny amount of carbs - about 2 grams for the entire recipe.
Heat the sauce over low heat and add the cheese slowly and gently to prevent it from becoming stringy.
Please don't skip the mustard - its acidity helps improve the sauce's texture.
You can keep the cheese sauce in an airtight container in the fridge for up to 4 days. When ready to use it, add a tablespoon of heavy cream and reheat it covered in the microwave at 50% power. Stir it after 30 seconds, then continue reheating - if needed - for 30 more seconds. You can also reheat it on the stovetop over low heat.
I don't recommend freezing this sauce, as it will likely become grainy or separate upon thawing.