Remove the leaves from the chard and blanche them in a pan of boiling water - cook them for around 1-2 minutes until soft and the leaves darken slightly. Remove the leaves, allow to cool and drain well by squeezing out excess liquid. (If you like, you can place them in cold, iced water after cooking to help keep a slightly brighter color, and cool quicker, but I don't think it's that needed.)
Squeeze out any excess liquid from the chard more than once then roughly chop. Put the chard and basil in a food processor and pulse to break up well. Then add the almonds and lemon zest, pulse again to chop and mix, then add the creme fraiche and parmesan. Finally add the olive oil in a steady stream with the food processor running and pulse until smooth and well blended together.
Use as you would other pestos eg with pasta, spread in sandwiches etc.