In bowl of food processor, add pistachios and process on high speed, scraping down sides as needed. Continue processing until a thick, oily paste forms, about 5-7 minutes.

Add sugar, water and spinach (if using) and continue processing until smooth and well-combined, about 1-2 minutes more.

In medium saucepan, whisk pistachio paste, sugar, cornstarch and salt.

Gradually whisk in almond milk. Continue whisking until all lumps have dissolved.

Cook over medium heat, whisking frequently, until mixture comes to a low boil. Continue whisking and boiling until thickened, about 3 minutes. Pudding will continue to thicken as it cools.

Remove from heat. Stir in almond extract.

Pour pudding into small serving bowls. Cover with plastic wrap, then pat down gently so plastic touches the pudding. (Note: This prevents a rubbery 'skin' from forming on top.)

Transfer to refrigerator. Chill at least 2-3 hours, or until set.

To serve, garnish with crushed pistachios, coconut whipped cream and green sugar. Fresh fruit or chocolate chips work well, also.