Make filling: Stir together chicken broth and mustard in a saucepan until well combined. Bring to a simmer over medium-high heat, then add cream and butter.

Reduce heat to medium and simmer until reduced by half. Stir in crab and shrimp; keep warm over low heat.

Make sauce: Stir together cream and mustard in a small pot over medium heat until hot. Whisk in Cheddar cheese until smooth. Season with nutmeg, salt, and pepper; keep warm over low heat.

Prepare omelets. Grease an 8-inch nonstick skillet with cooking spray and place over medium heat. Whisk together eggs, cream, salt, and pepper in a medium bowl until smooth.

Pour about 1/4 cup egg mixture into the hot pan; swirl to make a thin, even layer. Cook until firm, then flip and cook for a few more seconds to firm the other side.

Spoon 1/6 of the seafood filling onto the lower half of omelet, then roll up into a cylinder. Repeat this step with remaining egg mixture.