Prepare beef. Combine 2 tablespoons olive oil, brown sugar, fish sauce, soy sauce, lemongrass, garlic, Thai chili, coriander, salt, and pepper in a food processor or blender. Puree until smooth. Pour marinade over beef, mixing gently to coat. Let sit for 1 hour or up to overnight.

Meanwhile, make dipping sauce. Combine hot water and brown sugar in a small bowl, stirring until sugar has dissolved. Add fish sauce, tamarind paste, lime juice, and chopped cilantro, stirring until combined. Set aside.

Beat eggs in a shallow bowl and add flour to another shallow bowl. Coat the slices of rib eye in flour, shaking off the excess. Dip in beaten eggs, making sure to coat all sides.

Heat 2 tablespoons oil in a large saute pan over medium heat. Lay beef in an even layer in the pan and cook until golden brown. Flip and cook until golden brown on the other side. You may have to cook the beef in batches.

Remove beef from the pan and transfer to a serving platter. Serve with dipping sauce and rice on the side, if desired.