Whole Wheat Sticky Toffee Date Cake

Name: Whole Wheat Sticky Toffee Date Cake
Ingredients: For the cake:; 12 tablespoons unsalted butter at room temperature, plus more for the pan; 8 ounces pitted dates, chopped; 1 tablespoon fresh lemon juice; 1/3 cup unsweetened applesauce; 1 1/2 cups 100% whole wheat flour such as Community Grains Whole Wheat Flour; 1 teaspoon baking soda; 1 teaspoon ground cinnamon; 1/2 teaspoon ground cardamom; 1/4 teaspoon ground ginger; 3/4 teaspoon fine sea salt; 1/2 cup coconut palm sugar or light brown sugar; 2 large eggs; 1/2 teaspoon vanilla extract; chopped toasted walnuts, optional; For the sticky toffee; 1/4 cup brown rice syrup or agave nectar; 1/4 cup honey; 1/2 cup coconut sugar or light brown sugar; 1/4 teaspoon fine sea salt; 2 tablespoons unsalted butter; fleur de sel