Ham and Cheese Crepes

Add flour, milk, eggs, and melted butter to a blender and process until smooth, 1 to 2 minutes.

Set batter aside for at least 20 minutes.

Heat 1 teaspoon butter in a skillet over medium heat.

Cook onions, stirring occasionally, until they start to turn golden brown, about 5 minutes.

Coat a crepe pan or nonstick skillet over medium heat with about 1 teaspoon of the melted butter.

Ladle about 1/4 cup batter into the pan, swirling the pan to thinly coat the entire bottom.

Cook until small brown spots appear on the bottom of the crepe, about 2 minutes.

Loosen crepe carefully from the pan using a spatula and gently flip to brown the other side, 1 to 2 minutes more.

Slide crepe onto a plate.

Repeat with remaining batter, buttering the pan as needed and stacking crepes between pieces of parchment or waxed paper.

Assemble crepes, one at a time, in the still-warm pan; spread some mustard over one half, cover mustard with some ham slices, and top with Gruyere cheese.

Fold the other side over the filling, pressing down slightly, and heat briefly just until the cheese starts to melt.

Fold crepe in half again.

Each finished crepe should end up about 1/4 the size of the original.