Grind the nuts. Combine all the ingredients, except the flaky sea salt in the bowl of a food processor fitted with the blade attachment. Blend on medium speed until mixture holds together when you squeeze it. Have patience this can take up to 15 minutes. Stop the food processor every few minutes to scrape down the sides so the mixture blends evenly. 

Form into the round shape. Dip a 2-inch wide biscuit cutter in powdered sugar. Scoop a tablespoon of the nut mixture into the mold and press down to make a firm, even, round disc. Gently remove cutter. Repeat with remaining mixture. 

Garnish and wrap. Sprinkle mazapan with crushed pistachios and flaky sea salt then wrap each mazapan individually with tissue paper or serve immediately. 

Store. Mazapan keep well in a tightly-sealed container for up to a week or in the freezer for up to 3 months.