In a large bowl, combine fresh lemon juice, corn starch, ground cumin, and a portion of the ground turmeric, garam masala, and salt. Toss the cauliflower florets in this mixture until they are evenly coated.

Heat olive oil in a large skillet over medium-high heat. Add the coated cauliflower florets and sauté for 7-8 minutes until golden brown and tender.

Reduce heat to medium, add remaining olive oil and unsalted butter. Toss in the chopped yellow onion and cook until translucent, about 8 minutes. Stir in garlic, ginger, and tomato paste and cook for 2 minutes.

Add the remaining spices (ground turmeric, garam masala, salt, paprika, ground cinnamon, and optional cayenne pepper) to the skillet. Cook for about 1 minute while stirring constantly.

Pour in the canned tomato sauce and vegetable broth. Bring to a boil, then reduce heat to low and let it simmer. After 5 minutes, add the heavy cream and return the sautéed cauliflower.

Remove from heat and garnish with chopped cilantro. Serve over basmati rice, with Greek yogurt on the side.