The garlic should soften and smell fragrant. Avoid cooking it till it turns brown.
You should notice the roux start to thicken up and darken a bit in color.
The sauce should still be bubbling gently. At no point should you boil the sauce.
You should notice a lot of evaporation as the sauce reduces to about half of the volume. Stirring frequently will help prevent scorching, or burning.
Blending the sauce will also smooth out any lumps of roux you might not have whisked completely.
Consider topping with: red onion, mushrooms, spinach, bacon, artichoke hearts, chicken, or broccoli.
If using it in pasta, consider grating the zest of a lemon into your sauce. This will add a citrus note and cut some of the richness.
Toss a little sauce into a seafood pasta for an even better combination.
