In a large wok or skillet, drizzle the 2 tablespoons (30 milliliters) vegetable oil over medium high heat.
Add half of the chopped onion and cook, stirring occasionally, until softened and starting to turn golden.
Stir in the garlic and the curry powder, then cook until fragrant, another minute.
Add the ground beef and continue to cook, breaking it up into small pieces with a wooden spoon or spatula, until golden and no pink remains.
Season with the sugar, salt, and white pepper. Adjust seasonings to taste.
Stir in the remaining chopped onion and the green onions.
Remove from heat and transfer the mixture to a large bowl. Cool to room temperature.
Once cooled, fold the eggs into the meat mixture until evenly combined.
In a small bowl, whisk together the cornstarch and water. Set aside.
Place a large skillet over medium heat and fill with a thin layer of vegetable oil.
Line a large plate with paper towels.
Place one spring roll wrapper on a work surface with the corner facing you (take care, the curry powder may stain) and cover the others with a towel to keep them from drying out.
Place about 1/4 cup (60 milliliters) of the beef and egg mixture in center of wrapper in an even layer. Brush the edges with the cornstarch slurry.
Fold the bottom corner up over the filling, then the left and right corners.
Fold the top corner down and lightly press to make a parcel.
Carefully transfer the formed pancake, seam side down, to the heated oil and fry until golden.
Carefully flip and fry the other side until golden and heated through. Transfer the cooked pancake to the towel-lined plate.
Repeat with the remaining wrappers and filling.
Serve the Martabak Telur hot with the vinegar sauce and optionally sweet chili sauce.