Reduce the heat to medium and add the butter to the same pot.
Add the broken vermicelli and cook, stirring frequently, until deep golden brown. Watch it closely so it doesn't burn.
Add the onion and cook until softened.
Add the garlic and cook briefly, just until fragrant.
Stir in the basmati rice, Lebanese seven spice, cinnamon and kosher salt. Cook for about 1 minute, stirring to coat the rice in the butter and spices.
Pour in the chicken broth and scrape up any browned bits from the bottom of the pot.
Return the chicken thighs to the pot, nestling them into the rice.
Bring to a gentle simmer, then reduce the heat to low and cover.
Cook for 17 to 20 minutes, until the rice is tender and the chicken is cooked through to 165°F.
Remove from the heat and let stand, covered, for 10 minutes.