Finely chop the herbs then add them into a bowl with the eggs and salt. Whisk them together well so that the eggs are well broken up - using a fork can be easier to save the pieces of herbs getting caught up in a whisk, but both work.
Warm a small skillet/frying pan (around 8 in/20cm) over a medium-low heat. Add the butter and let it gradually melt and start to foam slightly - it should be a slow melt, not a fast sizzle.
Add the egg-herb mixture to the skillet and use a fork to move the mixture around, break up the curds as they form and incorporate the butter into the eggs. You also want to try to stop the eggs sticking too much. Scrape down any bits of egg that stick to the side.
Gradually cook the eggs - it will almost certainly take longer than you expect unless you are well practiced - and stop stirring as more of the eggs start to firm up. Once the edges are cooked but it is still slightly soft in the middle and on top, loosen the edge and lift up to make sure it isn't stuck, then fold in one side. You can either fold in both sides then roll it on to the plate, or you can roll a few times from one side then slide onto a plate. You want it to be at least folded in thirds, or a little more if you prefer, but it doesn't need to be tight.
Serve immediately, either on it's own or it's also good with a lightly dressed green salad.
Notes
You can mix the balance of quantities of herbs in this, but you want around 2tbsp (chopped volume) overall. Traditionally, the mix also includes chervil but I find that pretty hard to find, if ever.