Cut a piece of parchment paper to fit the bottom of the pan. Spray a loaf pan (8 1/2" x 4 1/2" x 2 1/2") liberally with non-stick vegetable spray. Lay the parchment paper in the bottom of the pan and spray again. Set aside.
In a mini-prep food processor add the walnuts and 1tablespoon of the sugar. Pulse until the walnuts are finely ground. Transfer the nuts to a medium bowl and add the flour, baking powder and salt. Whisk to combine and set aside.
In a glass measuring cup add the whipping cream. Drop spoonfuls of the sour cream into the whipping cream until it measures 1 cup. Add the vanilla and whisk to combine. Set aside.
In a large bowl add the butter and remaining sugar. Cream the butter and sugar together until light and fluffy, about 4-6 minutes, scraping the sides of a bowl with a rubber spatula occasionally. Add the eggs one at a time and beat into the butter mixture until fully incorporated before adding the second egg. Beat until blended.
Add one third of the flour mixture and mix on low speed until just combined. Add 1/2 of the cream mixture and mix until just combined. Follow in the same manner with 1/3 flour, the rest of the cream and finally the last of the flour. Do not over mix.
Use your spatula to scrape the bottom and sides of the bowl to make sure that everything has been evenly incorporated. Pour the batter into the prepared loaf pan and smooth the top. Sprinkle the top of the loaf evenly with demerara sugar, if desired for a slightly crunchy top.
Bake for 50 minutes to an hour or until a cake tester comes out clean.
Let the loaf rest in the pan for about 20-30 minutes before inverting onto a rack. Remove the parchment paper and flip the loaf right-side-up to continue cooling.