Begin by patting the boneless chicken thighs dry with paper towels to remove excess moisture. In a shallow dish, combine flour and cornstarch, then coat each chicken thigh evenly with the mixture. Let the coated chicken rest for about 10 minutes to ensure the coating adheres well.

Heat a generous amount of cooking oil in a skillet over medium-high heat, aiming for a temperature of around 350°F (175°C). Carefully place the coated chicken thighs into the hot oil, searing them for 5-7 minutes on each side until they turn a beautiful golden brown. Use tongs to flip the chicken, ensuring it cooks evenly. Transfer the chicken to a paper towel-lined plate.

In a separate saucepan, combine soy sauce, sugar, minced garlic, and freshly grated ginger. Heat the mixture over medium heat, stirring occasionally, until it begins to simmer, about 3-5 minutes.

Add the fried chicken thighs to the saucepan. Gently toss the chicken in the sauce until every piece is evenly coated, allowing the flavors to envelop the crispy exterior. This should take about 2 minutes.

Plate the crispy chicken generously and top each serving with crispy fried jalapeño rings for extra flair.