In a medium sauté pan, heat 1 tablespoon oil over medium-high heat. Add onion, garlic, salt, and pepper; cook until onion is translucent. Transfer onion mixture to a heatproof bowl.
Add remaining 2 tablespoons oil to pan, and heat over medium-high heat. Add mushrooms; cook until fragrant, approximately 3 minutes. Add thyme, mint, tarragon, and onion mixture; cook for 2 minutes. Transfer mushroom mixture to a heatproof bowl. Let cool to room temperature.
In a medium bowl, beat together blue cheese and ricotta cheese with a mixer at low speed until combined.
Divide cheese mixture and mushroom mixture among Buckwheat Crackers.
Garnish each canapé with a fresh thyme sprig, if desired. Serve immediately.
Recipe by TeaTime Magazine at https://teatimemagazine.com/herbed-mushroom-buckwheat-canapes-recipe/