This is best done using a good blender like this one or an immersion blender like this one. Start by pureeing your flour, sugar, salt, milk, eggs, and butter until completely smooth. When you have a well-combined mix, refrigerate it for at least 30 minutes before beginning to cook. This allows the butter to harden just a little bit, giving you better crepes.
When you’re ready to cook, heat an 8-inch skillet (or crepe pan) over medium heat. When the skillet is hot, lightly coat it with butter before quickly pouring 1/4 c. of batter into the middle of the pan. Then in a swift manner, swirl the batter around so that it evenly coats the bottom of the skillet. Allow to cook for 1-2 minutes until golden and the edges begin to lift. Gently flip the crepe (you can use your fingers or a spatula) and cook on the second side until set and golden, about 30-45 seconds. Allow crepes to cool on a plate after brushing with butter.
Continue until you’ve used all your batter and have a nice stack of crepes. You can serve them hot or room temperature depending on what you’re using as a filling.