Cut chicken thighs into bite-sized pieces. In a bowl, whisk the egg with salt and pepper. Add the chicken pieces and toss to coat evenly. In a separate shallow dish, combine cornstarch and all-purpose flour. Dredge the coated chicken pieces in the flour mixture, ensuring each piece is well-covered. Set aside.

Heat vegetable oil in a deep wok or pot over medium-high heat to about 177 °C (175 °C). Carefully fry the chicken pieces in batches, ensuring not to overcrowd the pot. Fry for about 4-6 minutes per batch, until golden brown and cooked through. Remove chicken with a slotted spoon and drain on paper towels.

In a clean skillet or wok, melt the butter over medium-low heat. Add the minced garlic and sauté until fragrant, about 30 seconds. Be careful not to burn the garlic.

Add the sliced red chilies (if using) and curry leaves to the skillet. Sauté for another 30 seconds until the curry leaves are fragrant.

Stir in the mashed salted egg yolks. Cook, stirring constantly, until the mixture becomes foamy and slightly thicker, about 1-2 minutes.

Pour in the heavy cream and stir well to combine. Add the sugar and a pinch of salt if needed (salted egg yolks can be quite salty already). Continue to cook, stirring, until the sauce thickens to a glossy consistency that coats the back of a spoon.

Add the fried chicken pieces to the skillet with the salted egg glaze. Toss gently but quickly to ensure each piece is evenly coated. Serve immediately.