I've used arrowroot, cornstarch, extended simmering, etc. in the past for thickening in the past with mixed results. Then I discovered xanthan gum around 15 years ago and it's the only thickener I've used since and recommend. It's a non-fail and fast thickener that doesn't alter the taste or color of what it's used in. It can be used in both hot and cold liquids with no change in the outcome. It's most commonly used in dressings and sauces, but also has applications with bakery products. Check the label of many commercial salad dressings and sauces and you'll often see xanthan gum as an ingredient.
The most readily available commercial brand for most is "Bob's Red Mill". For me, the dominant local super market chain, Marianos, a Kroger affiliate, carries it as does my neighborhood Whole Foods Market. I've heard that Target and Walmart also carry it but I never shop at either of those stores.
One warning, a little bit of the product goes a very long way. Follow the package instructions, and if you've never used xanthan gum before use the minimum suggested dosage. Stir well for 4-5 minutes, and if you're satisfied with the outcome, stop. If not, add a wee bit more and repeat the process until you achieve the results you're seeking.