For serving: rye breadsourdough, dinner rolls, bagels
Allow the butter to soften slightly at room temperature. The butter should be barely softened, but not at all warm. Place the poppy seeds, sesame seeds, garlic, and onion in a flat bottom dish. Gently roll the butter through the spice mixture to coat completely. Place on a serving tray or in a butter dish. Serve with the breads of your choice. Enjoy!
For ease of serving, or personal preference, you can also blend the spices with the soft butter. I've made the butter both ways and don't have a preference. Both methods work well.