Instructions

1. 1
   If using onion powder and dried tarragon, combine them with 2 tbsp water in a microwaveable measuring cup or small bowl. Microwave for about 6 seconds, then set aside.
2. 2
   Soften the butter in the microwave, stopping the oven every 5 seconds to mash and stir the butter until it is very soft but not liquid.
3. 3
   In a small bowl or glass measuring cup, microwave the mayonnaise for 5 seconds.
4. 4
   Remove mayonnaise from the microwave, and beat in the butter a teaspoonful at a time.
5. 5
   Stir in the onion, tarragon, and pepper.
6. 6
   Test the temperature; if it is not warm enough, heat it for 6 seconds at a time in the microwave, stirring each time. Do not overheat or it might separate; it should be warm not hot.