Preheat the oven to 325°F (163°C). Grease and flour two 8-inch (20-cm) cake pans. Set aside.
Sift together flour, baking powder, and salt in a large bowl. In a mixer, cream butter and sugar until fluffy, about 6 minutes.
Add maple syrup, egg yolks, milk, and vanilla, mixing for another 2–3 minutes. Gradually add dry ingredients, mixing until smooth. Fold in chopped walnuts.
Whip egg whites with cream of tartar in a separate bowl until stiff peaks form (about 6 minutes). Gently fold the whipped egg whites into the batter until just combined.
Divide batter evenly between the pans and bake for 30 minutes, or until a toothpick inserted in the center comes out clean.
Let the cakes cool in pans for 10–15 minutes, then transfer to a wire rack to cool completely.
For the frosting, beat cream cheese, butter, powdered sugar, vanilla, and salt in a mixer until smooth (6–8 minutes).
Frost the cooled cakes by spreading half the frosting on one layer, then layering and frosting the top.
Decorate with walnuts, fresh fruit, and edible flowers. Serve at room temperature.