1. In a food processor, pulse the fresh spinach until finely minced. Add the butter, egg and parmesan cheese and pulse until combined. Add the in the salt, then flour, 1/2 cup at a time, pulsing slowly until a dough begins to form.
2. Scoop the ball of dough out of the food processor and wrap it tightly in plastic wrap. Store it in the fridge for at least 1 hour to allow it to completely chill (this will prevent your crackers from spreading).
3. Preheat the oven to 350 F and line two baking sheets with parchment paper or a silicone baking mat. On a lightly floured surface, roll out half of the dough to about 1/4″ thickness, ensuring it is the same thickness all over. Using whichever cookie cutter you’d like, cut out the crackers and place them on the baking sheet; they will not spread so you can put them fairly close together.  Repeat with more flouring and rolling, until all of the dough is used up.
4. Bake the crackers for about 10 minutes, until the edges just start to turn brown. Remove from the oven and after cooling for 5 minutes, remove the crackers to a wire cooling rack until completely cooled.

Crackers can be stored at room temperature, in an airtight container, for about 1 week. You can also freeze them for up to 2 months, thawing at room temperature before eating.