In a pan on medium heat, melt butter.
Add onion, mixing into butter.
Once the onions begin the soften, add garlic, thyme and rosemary.
Saute for a couple of minutes.
Sprinkle about a tbsp of flour, mixing in.
Once mixed in, add wine.
Reduce until alcohol has burned off and the reduction is thick enough to coat a spoon. Taste reduction to ensure alcohol has burned off.
Spread reduction on each slice of bread.
Butter the outside of each slice.
Grill in a pan on medium heat until golden brown on each side.