Grease heavily the back of a big heavy bottomed pizza pan or thali and rolling pin, with two tbs spoon oil. (See notes)
Dry roast sesame seed in heavy bottomed pan on medium low flame for 3-4 minutes with constant stirring.
Keep a bowl with water ready for testing jaggery.
Put grated jaggery in a heavy bottomed wok. Melt jaggery on medium flame, while stirring constantly. When jaggery is melted, add oil in wok along the side of wok.Take the flame to medium high so jaggery start bubbling and caremelizing.
Turn of the heat, stir well so jaggery is uniformly caramelized.
Test jaggery in water by dropping a small drop and then press it. If the drop form a soft lump, cook more. If it turns hard immediately then your jaggery is ready.
Mix in roasted sesame seeds and quickly pour all mixture on greased thali. With greased rolling pin make 1/8 inch flat sheet.
Apply a thin layer of oil on top of brittle for glaze. Make cutting marks while the brittle is still hot. Let the brittle cool completing before removing from thali.
Store in airtight container at room temperature.