In a bowl, whisk ricotta and gulkand until mostly smooth. A few small ricotta grains are fine.
Line an 8×8 inch pan with parchment, leaving overhang on two sides.
Place a wide, heavy pan on medium heat. Add the ricotta-gulkand mixture and the paan milk from the blender. Add milk powder and cardamom if using. Stir constantly until loose and glossy, about 2 minutes.
Reduce heat to low-medium. Cook, stirring often, until the mixture thickens noticeably, about 8 to 10 minutes. It will still look pourable.
Continue on low-medium, stirring continuously, until the mass pulls away from the sides and a spatula pressed flat on the surface lifts away clean with no wet streak, about 14 to 18 minutes more (22 to 28 minutes total cook after the pan step). Stir in green gel color now if using.
Immediately scrape into the lined pan. Spread evenly. Tap the pan once on the counter to release air pockets.
Sprinkle candied fennel, rose petals, and pistachios on top while still warm. Press gently so they stick.
Cool on the counter 20 minutes, then refrigerate uncovered until firm enough to slice, at least 2 hours (3 hours for cleaner edges).
Lift out using parchment overhang. Cut into 18 squares with a sharp knife wiped clean between cuts.