This is a question for my own general learning purposes, as I'm somewhat new to baking with chocolate. In step 3, it tells us not to stir the choc...

I've never seen a technique like the one Slater uses to melt the chocolate, add the espresso and then melt and mix the butter - it's fascinating and I want to try the recipe. In general, when melting chocolate, it's best not to stir it too much. In part it's not to stir air into the chocolate and, I was once told by a French pastry chef, that if you stir chocolate too much, you lighten its color. I think the higher the cocoa content, the less stirring you want to do. In any event, if you are melting the chocolate over barely simmering water, and if the water is not touching the bottom of the bowl, you shouldn't have to stir - the chocolate will melt slowly and evenly. That said, I always keep my eye on the bowl and stir gently a couple of times.

I think that you don't stir at all in step 3 because you don't want the chocolate to seize. Chocolate is melting over simmering water. If even a drop of water gets added to hot melted chocolate, it might seize. Same reasoning in step 4, you only stir one to mix in the butter which has a bit of water in it. That's my best guess as to why the no stirring.

I don't stir chocolate when melting it. It's important to keep an eye on it (and a low flame) so it doesn't scorch, but not to stir.