1. Cube 10 tablespoons of Kerrygold Salted Butter and place in bowl of food processor. Add flour and pulse until mixture resembles small grains. Turn processor on and slowly pour in water. Process until dough comes together and forms a large ball.
  2. Remove dough from bowl and place on a lightly floured surface. Shape into a 5-inch disc and wrap in plastic. Refrigerate for 30 minutes.
  3. Warm oil in large skillet over medium heat. Add onion and saute until almost translucent. Stir in mushrooms and remaining two tablespoons of Kerrygold Salted Butter and cook until mushrooms have softened and released most of their juices. Stir in garlic and thyme and cook for another minute. Remove from heat and season to taste with salt and pepper.
  4. Preheat oven to 400°F. Line a large baking sheet with parchment.
  5. Lightly flour your work surface. Remove dough from refrigerator and roll into a large 12-inch circle. Transfer dough to prepared pan. Evenly spread mushroom filling on dough, leaving a 2-inch border around the edges.
  6. Fold edges over filling, pleating the dough as needed.
  7. Whisk egg with 1 tablespoon water. Brush dough edges with egg wash. Bake for 40 minutes.
  8. Remove galette from oven, sprinkle with Kerrygold Swiss Cheese and bake for another 5 minutes or until cheese is melted.
  9. Allow to cool for 5 minutes. Sprinkle with fresh thyme. Cut into wedges and serve warm.

Recipe by Garnish with Lemon