Spray an 8 1/2-by-4 1/2-inch loaf pan with cooking spray and line it with parchment paper, leaving an overhang. Heat the oven to 300 F.
Combine the flour, salt, and soda in a bowl and whisk to blend; set aside.
In a mixing bowl with an electric mixer, beat the butter and sugar together for 4 to 5 minutes or until light in color and fluffy. Scrape the sides of the bowl occasionally. A stand mixer is easiest, but you can use a handheld mixer.
Add the vanilla and almond extract and beat just to blend. Add the eggs, one at a time, beating each one until thoroughly incorporated into the batter.
Add 1/3 of the flour mixture and half of the buttermilk and beat until blended. Repeat with another 1/3 of the flour mixture and remaining buttermilk, then beat in the remaining flour mixture.
Transfer about half of the batter to a medium bowl. Combine the Dutch cocoa powder and hot water and whisk until smooth. Fold the chocolate mixture into the medium bowl of batter.
Spoon both batters into the pan, alternating between colors. Use a knife or spatula to swirl the batter to make a marble pattern.
Bake the cake for 1 hour and 5 minutes to 1 hour and 15 minutes or until a cake tester or toothpick inserted into the center comes out with just a few crumbs clinging to it.
Cool in the pan on a cooling rack for 20 minutes, then turn the cake out onto the cooling rack to cool completely.