Mix the flour with the milk. Add the eggs and stir in the salt. Melt the butter and add it. Mix everything into a creamy, slightly runny batter. Place the dough in the refrigerator for about 1 hour to swell.
Cut the ham and Gouda cheese into strips. Heat up a crepe pan and add a ladle of batter. Spread the dough evenly in it. When the dough is dry and bubbling, turn it over. Place the Gouda cheese and ham on top alternately. When the cheese starts to melt, roll up the crepe and keep it warm.