Heat ghee in a medium-size Dutch oven over medium until shimmering. Add onion, and cook, stirring often, until golden brown and very soft, about 8 minutes.
Add garlic and ginger to Dutch oven; cook, stirring often, until fragrant, about 1 minute. Stir in tomato paste, chile powder, cumin, coriander, turmeric, salt, cardamom, and Thai chile (if using). Cook over medium, stirring continuously, until mixture thickens and darkens slightly, 3 to 4 minutes, adding 1 tablespoon water, as needed, to prevent mixture from burning or sticking to bottom of Dutch oven. Remove from heat, and let cool until just warm, about 5 minutes.
Transfer onion mixture to a blender. Secure lid on blender, and remove center piece. Place a clean towel over opening. Process until light in color, about 30 seconds. With blender running on medium speed, slowly pour 1 cup water through opening; process until mixture is smooth, 1 to 2 minutes. Return sauce to Dutch oven; stir in peas, heavy cream, and paneer. Bring to a simmer over low; cook, stirring gently and often, until peas are cooked through and paneer is tender, about 10 minutes. Sprinkle with cilantro; serve with rice.
