In a small saucepan, melt the butter without letting it brown. Then remove it from the heat and let cool.
In a bowl, briskly whisk the eggs, then gradually add the flour, a pinch of salt, the rum and melted butter. At this point, slowly add the milk while whisking. Continue whisking until you have a smooth batter without clumps. Let rest for 20 minutes.
Heat a non-stick pan or crepe griddle. Once hot, brush on the pan with the melted butter. Use a ladle to add enough batter to cover the entire pan. Try to make the thickness even across the pan.
When the crepe begins to separate itself from the pan, flip the crepe quickly using a spatula and cook the other side.
Bubbles will begin to form as the egg cooks and the golden color is an indication that the crepe is perfectly cooked.
Once you have cooked both sides, place the crepe on paper towels. Continue making crepes until you have finished the batter.
Let cool slightly before filling. The crepes can be filled with cheese, sliced meats or sour cream.