Chop the shallot or onion and mince or grate the garlic. Warm up the dairy, just enough so it's not cold, to help prevent separation.
Make the sauce:
Heat a large pan over medium-high heat. Once hot, melt the butter. Add the chopped shallot (or finely chopped onion) and lemon zest and sauté for 2 minutes, until it’s translucent and golden. Add the garlic and sauté it for about 30 seconds until fragrant. Add the chicken broth and stir to combine.
Add the warmed cream to the pan and stir until the mixture comes to a simmer. Add the thyme (or Italian seasoning) and stir. Reduce the heat to low, add the lemon juice and stir, cover the pan with a lid, and simmer the sauce for 10 minutes.
Check on the sauce. For a thicker sauce, make a slurry with 1 tablespoon cornstarch + 3 tablespoons of water in a small dish. Add it to the sauce, stir, and simmer for 2 more minutes. If you used cream and like the sauce as is, you're good to go.
Serve:
Toss this lemon garlic sauce with cooked pasta or over your favorite protein.
Notes
Swap the shallot for ¼ of cup finely chopped onion (about ½ small onion).
If you want to use garlic powder, use 2 teaspoons instead of the whole garlic cloves.