Preheat the oven to 350°F. Butter 1 9-inch round cake pan or 1 loaf pan. Line the bottom of whichever pan you chose with parchment paper, and then butter and flour the interior, including the paper at the bottom, too.
In a medium sized bowl mix together the 1 1/4 cups flour, salt, baking powder and baking soda.
In another medium sized bowl cream together the butter and 2/3 cup sugar with an electric mixer for about 3 minutes until the mixture is smooth. Blend in the eggs one at a time, making sure each is fully incorporated. Blend in the vanilla, 1/3 cup orange juice and zest.
Blend the dry ingredients into the creamed mixture in three batches, beating on low speed just until the flour is incorporated. The batter may look a little grainy, which is ok.
Scrape the batter into the pan and smooth the top. Bake for about 25 minutes for a 9-inch cake, and 40 to 45 minutes for a loaf cake, until a wooden skewer inserted into the middle comes out clean. Cool in the pan on wire racks for 15 minutes then turn the cake out of the pans, peel off the paper, and turn it upright to finish cooling on the racks.
While the cake is baking, make the optional Orange Syrup. In a small bowl stir together the 3 tablespoons orange juice and ¼ cup sugar. The sugar may not become fully dissolved in the syrup, which is ok.
As soon as you remove the cakes from the pan and flip them upright on the wire racks, give the orange syrup a very good stir and brush half of it over the top of the cake. Allow it to soak in for several minutes, then brush the rest of the glaze over the top and sides of the cake. Allow to cool completely. Slice and serve.
Notes
If you want to make a layer cake, double the recipe, divide the batter between 2 9-inch pans, and bake according to directions. You can frost between the layers, and on the sides and top as you would for any layer cake.