Preheat the overn to 350 degrees.
In a large mixing bowl combine all of the Handvo batter ingredients until everything is incorporated well. Set it aside and make the tadka.
For the tadka, heat a small vessel/pot over high heat and add your oil. Once the oil is hot, add the mustard seeds. Once the mustard seeds start to pop and crackle, add the cumin seeds and hing, let them splutter, then add in the red chilis, give it a quick (and careful) swirl and remove from heat (the red chilis brown fast so you dont want it over the flame for too long or they will burn). Pour this mixture directly into the handvo batter and mix well.
Pour the batter into a greased 9x 13 oven dish. Drizzle one tbsp of oil over the top and sprinkle with the sesame seeds evenly across the surface.
Place in the oven in the middle rack for about 50 minutes to one hour. The handvo is done when a toothpick inserted in the center comes out clean.
Once the handvo is cooked all the way, set the oven to a low broil setting for about 3-4 minutes to brown the top of the handvo. Keep an eye on this so it doesnt brown/burn too quickly.
Remove from the heat, let it sit for about 5 minutes and then use a sharp knife to cut into squares. Serve hot with a cold glass of milk, or a hot cup of chai and enjoy!