Preheat oven to 180c.
Spread panko crumbs on a rimmed baking sheet/tray in an even layer.
1¾ cups panko breadcrumbs
Bake for 7-10 minutes, stirring/shaking halfway through to redistribute.
When the panko is browned, tip most of the crumbs into a large dish ready for crumbing, transferring about ¾ cup into a separate bowl (for sprinkling).
Meanwhile, to make the dredging batter, mix together egg and plain flour in a dish, until no lumps remain.
1 egg, 2 tablespoon plain (all-purpose) flour
Add mayonnaise, dijon mustard, garlic powder and salt then mix well to combine.
1 tablespoon mayonnaise, 1 tablespoon dijon mustard, ½ teaspoon garlic powder, ½ teaspoon fine (cooking) salt
Dip one chicken thigh into the batter, turning with tongs to coat it (scraping off any excess).
4 boneless skinless chicken thighs
Then using the tongs, transfer the chicken to the large dish with the crumbs.
Shake over some of the crumbs from the "sprinkle" bowl to start the crumbing.
Using a spoon, pick up extra crumbs from around the chicken and sprinkle over chicken, pressing down to help them stick.
Transfer the chicken thigh to a baking tray fitted with a wire rack and then repeat with the remaining thighs.
Bake for 25-30 minutes or until chicken is cooked through.