A ristretto is very much an Italian way, simply restraining the amount of water and time that is to go into the making of an espresso, not to make it stronger, just to make it dense in flavor, and viscosity.
Knowing what I wanted with the sudden wish to infuse my second morning coffee shot with saffron, I understood it called for density, not meaning strength but a balanced concentration of flavor. And while ristretto refers to an espresso variation, it actually refers to enhancement through reduction. For this, an espresso is not a must. Just a focused pouring of water onto the coffee grounds in my Indonesian coffee filter.
Sila Blume 