Fill large pot with water. Add 1 tbsp salt. Bring to rolling boil. Add spinach in batches. Cook 30 seconds until wilted bright green. Immediately plunge into ice water bath.

Drain and Squeeze dry completely. Chop coarsely. This step locks in color.

Melt 2 tbsp butter in large skillet over medium heat. Add minced shallot. Cook 3 minutes until soft and sweet. Stir in garlic. Sauté 1 minute until fragrant. Don't let it brown. This aromatic base makes it restaurant-worthy.

Sprinkle flour over shallot mixture. Whisk constantly 2 minutes. Cook out raw flour taste. Should smell nutty. Slowly pour in warm milk while whisking.

Add heavy cream. Keep whisking until thickened. Sauce coats spoon back. Pure magic happens here.

Stir in nutmeg, salt, pepper, and cayenne if using. Taste sauce. Adjust seasoning. Fresh nutmeg gives that authentic steakhouse flavor. Simmer gently 2 minutes. Sauce becomes velvety smooth. Don't skip this essential step.

Add chopped spinach to creamy sauce. Fold gently until completely coated. Stir in remaining 2 tbsp butter. Cook 3 minutes until hot and glossy. Sprinkle Parmesan. Stir until just melted. Remove from heat immediately. Perfect texture achieved.

Transfer to warm serving bowl. Garnish with extra Parmesan sprinkle. Serve immediately beside perfectly cooked steaks. Steam rises invitingly. Family gathers around eagerly. Dinner magic complete!