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 stirring it in 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 over the steamed broccoli and serve.
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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, simply stir in a bit more cheese - try 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 stir the cheese in slowly and gently to prevent the cheese from becoming stringy.
Please don't skip the mustard - its acidity helps improve the sauce's texture.
You can keep the cheese sauce in the fridge, in an airtight container, for up to 4 days. When ready to use it, add a little heavy cream and reheat the sauce, covered, in the microwave at 50% power. Stir it after 30 seconds, then continue reheating - if needed - for 30 more seconds.