Maple Walnut Cake

Name: Maple Walnut Cake
Prep time: 20 min
Cook time: 30 min
Total time: 50 min
Cuisine: Canadian
Ingredients: 2 1/2 cups unbleached all-purpose flour; 1 tbsp. baking powder; 1 tsp. baking soda; 1/2 tsp. ground Himalayan pink salt; 1/2 cup unsalted butter, room temperature plus more for cake pans; 1/2 cup brown sugar; 3 large free-range eggs, room temperature; 1 cup good quality maple syrup; 1 tsp. pure maple extract; 1/3 cup buttermilk (tips & tricks); 3/4 cup walnuts, chopped and toasted; 1 cup walnuts; 3 tbsp. good quality maple syrup; 1 pinch fleur de sel; 1/2 cup unsalted butter, room temperature; 1/8 tsp. fleur de sel; 2 1/2 cups confectioners' sugar, sifted; 1/2 cup maple sugar, sifted; 7 to 8 tbsp. good quality maple syrup; 1/2 tsp. pure vanilla extract