Preheat the oven to 350 F. Grease and flour a 10-cup-capacity bundt pan.

Whisk flour, salt, baking powder, baking soda, salt and cardamom together in a medium bowl.

Pour buttermilk into a small bowl and stir in lemon juice.

In a large bowl, beat butter with a wooden spoon or a mixer until smooth, then beat in sugar until light and fluffy. Add eggs one at a time, beating well after each addition. Whisk in the vanilla.

Stir the butter mixture into the flour mixture in a few strokes, then add the buttermilk. Mix and fold until thoroughly combined, but be careful not to overmix.

Spoon one-third of the batter into the pan and smooth with a spatula. Sprinkle one-third of the walnut mixture overtop. Repeat two more times so that you end up with a good sprinkling of walnut mixture on top.

Bake for 50 to 60 minutes or until a skewer inserted in the center of the cake comes out clean.

Cool the cake in the pan for 10 minutes. Loosen the cake from the pan by running a slim knife around the edges of the cake, including the circle in the middle. Place a 10-inch plate overtop of the cake and invert it onto the plate. Remove the plate.

Next, place a wire cooling rack over the cake and invert the cake onto the rack so the side with the topping is facing up.

Cool the cake to room temperature before transferring it to a serving plate. Serve with a scoop of ice cream or just as is.