Line an 8-inch square pan with aluminum foil leaving overhang, spray with cooking spray; set aside.
In a large microwave-safe bowl, combine butter, honey, brown sugar, and heat on high power for 1 minute to melt.
Stop to stir. Mixture will be on the granular side, this is okay.
Return bowl to microwave and heat for 1 more minute on high power. Stop to stir
Return bowl to microwave and heat for 1 more minute on high power. Stop to stir. On this third and final burst, mixture will become quite bubbly and foamy; use caution when removing from micro because this is boiling hot caramel and can cause burns.
Stir in the vanilla using caution because mixture could bubble up.
Stir in the cereal.
Stir in the optional raisins (or nuts).
Turn mixture out into prepared pan, packing it down firmly with a spatula and smoothing the top.
Optionally, sprinkle evenly with sunflower seeds and salt (the salt cuts some of the sweetness and I recommend it).
Cover pan with a sheet of foil (to prevent fridge smells), and place pan in fridge to set up for at least 2 to 3 hours, or overnight, or until bars are completely set before lifting out with foil overhang, slicing, and serving.
Bars will keep airtight in the refrigerator for up to 2 weeks, or in the freezer for up to 6 months. I recommend storing them in the fridge rather than room temp because they soften and get loose.