Whole Wheat Date Walnut Cake

I was at a little coffee shop in London recently, and they had Date Walnut Cake on the menu, and it sounded so delicious to me, unfortunately, they were out. I couldn't stop thinking about how good it sounded, so I created my own recipe.
1) Preheat oven to 350 degrees Fahrenheit. Line bottom of 2 pound loaf pan with parchment paper, grease sides and bottom of pan.
2) Sift together flour, cornstarch, baking powder, salt, and spices in a medium sized bowl. Add maple syrup, sunflower oil, and soymilk. Stir together until well bended. Stir in dates and walnuts and pour into greased loaf pan.
3) To make the optional crumble topping, stir together flour and sugar. Cut in the vegan butter with a pastry blender or a fork until the mixture resembles crumbs. Mix in walnuts if desired. Sprinkle over top of batter in loaf pan.
4) Bake for 40 to 50 minutes or until cake springs back when pressed lightly in the middle. Let cool and turn out of loaf pan. Serve in 1/2 inch slices.
Note: The crumble topping is optional because it uses white flour and processed sugar. If anyone has a healthier recipe for crumble topping, please let me know :)
* I know maple syrup is expensive, so you can split 1/4 cup brown rice syrup and 1/4 cup maple syrup if you want :)
Also, you can leave out dates and walnuts for a delicious spice cake instead.
Source of recipe: I saw "Date walnut cake" on a menu at a cafe, and I decided to create my own version.