In a medium bowl, whisk together the honey, soy sauce, garlic, apple cider vinegar, garlic salt, and red pepper flakes (if using). Set aside.
To a large skillet over medium-high heat, pour in the chicken broth and heavy cream. Stir to combine and bring to a gentle boil.
Add the uncooked spaghetti to the skillet, fanning it out or breaking it in half if needed, so it lays mostly flat. Use tongs to gently stir and separate the noodles, making sure they’re coated and submerged in the liquid.
Reduce the heat to medium-low. Cover and simmer for 10-12 minutes, stirring occasionally, until the pasta is al dente and most of the liquid is absorbed.
In a small bowl, whisk together the cornstarch and water to make a slurry.
Pour the honey garlic sauce into the skillet with the pasta. Stir well, then immediately stir in the cornstarch slurry. Let simmer uncovered for 2-3 minutes, stirring often, until the sauce thickens and coats the pasta.
Remove from heat and sprinkle with Parmesan cheese.
Garnish with chopped parsley and extra red pepper flakes, if desired.