Mince the garlic. In a bowl, beat the eggs with the heavy cream, salt, and pepper until no streaks of white remain.

Melt half the butter in an 8-inch nonstick skillet over medium heat. Add the garlic and spinach and cook, stirring, about 1 minute until wilted. Transfer to a small bowl, press out the liquid with a spoon, and wipe the pan dry.

Lower the heat to medium-low and melt the remaining butter. When the foam starts to settle, pour in the eggs.

Stir gently with a spatula for 20 seconds, then let the eggs sit. Lift the edges and tilt the pan so uncooked egg flows underneath, until the omelet is set on the bottom but still glossy on top, about 2 minutes.

Scatter the spinach and crumbled feta over one half. Cook 30 seconds more, then fold the empty half over the filling.

Slide onto a plate, sprinkle with dill, and serve right away.