Place the butter in a small stainless steel skillet over medium heat. Let it melt, then continue cooking, swirling the pan every 20 to 30 seconds, until the foam subsides and the milk solids on the bottom of the pan turn golden brown, about 3 to 4 minutes. It should smell like toasted hazelnuts.

Add the sage leaves to the pan. They will crackle and crisp up in 60 to 90 seconds. Remove them with a slotted spoon as soon as the edges look lightly crisped - do not leave them in longer or they turn bitter.

Pour the brown butter into a small heatproof cup and let it cool for 2 minutes. Set the crisped sage leaves aside for garnish if you like.

Brew a double shot of espresso, about 60 ml. If using a moka pot, brew on medium-low heat and aim for a concentrated, dark pull.

Add the espresso, browned sage butter, and honey or maple syrup (if using) to a blender. If you're adding milk, add it now. Blend on high for 20 to 25 seconds until the mixture looks frothy and the butter is fully emulsified - no visible oil slick on the surface.

Pour immediately into a prewarmed cup. Top with one crisped sage leaf and a small pinch of flaky salt if you like. Serve right away.