Chanterelle mushrooms pie with cheese and herbs

Ingredients

• 200 grams (1 2/3 cups) whole wheat flour
• 1 teaspoon baking powder
• 1 egg yolk
• 0.5 teaspoons salt
• 100 grams (7 tablespoons) butter
• 2.5 tablespoons sour cream
• 1 large onion
• 400 grams (14 ounces) chanterelles
• 300 grams (1 1/4 cups) sour cream
• 125 grams (1 1/4 cups) hard cheese
• Butter for frying
• 0.5 teaspoon dried thyme
• Salt to taste
• Black pepper to taste