Combine agar-agar with 2 tablespoons of lukewarm water. Whisk it well.
Allow it to bloom for 5 minutes.
Meanwhile, heat heavy cream in a saucepan over medium-high heat. Allow it to simmer for a minute over medium heat.
Add bloomed agar-agar to cream and allow it to simmer for about 5 minutes (over medium-low heat) until it is completely dissolved. This process will hydrate agar-agar, which will facilitate it to set well. After 5 minutes, take it off the flame. The cream will become slightly thick.
Pour this mixture over chocolate chips and whisk until chocolate is completely melted. Set aside to cool to about room temperature. Keep stirring occasionally.
Add a few drops of green color and pistachio essence. Whisk it well.
While the above mixture is cooling, prepare the whipped cream by combining heavy whipping cream+powdered sugar +cornstarch. Beat until stiff peaks forms.
Pour the cooled chocolate mixture into whipped cream.
Fold gently until well combined.