Preheat the oven to 350 degrees Fahrenheit and grease a 9 x 5-inch loaf pan with nonstick cooking spray and line it with parchment paper. Set aside.
In a large bowl, whisk together 1 ¾ cups all-purpose flour, 1 (3.4-ounce) box instant pistachio pudding, 1 teaspoon baking powder, and ¾ teaspoon salt.
In the bowl of a stand mixer or a large bowl, cream together 1 cup softened butter and 1 ¼ cups granulated sugar until light and fluffy, about 3-4 minutes.
Add 4 large eggs one at a time, blending well after each addition. Add ½ teaspoon almond extract and ½ cup buttermilk and beat until combined.
Add the dry mixture to the wet mixture and mix until just combined.
Remove 1 cup of the batter and place it in a small bowl. Mix ¼ cup cocoa powder with ¼ cup hot water until smooth. Pour the cocoa mixture into the ½ cup of batter and mix until it is just combined.
Alternate the two batters in the loaf pan, starting with the pistachio batter. Add ⅓ of the batter to the bottom of the pan. Dollop half of the chocolate batter on top. Repeat with another ⅓ of the pistachio batter. Dollop the remaining half of the chocolate batter on top. Finally, add the remaining ⅓ of the pistachio batter. Use a knife or skewer to swirl the batter together by dragging the knife through the pan in a zig-zag motion. Turn the pan 90 degrees and repeat.
Top the batter with ¼ cup chopped pistachios and bake for 55-60 minutes, or until the top springs back when pressed and a toothpick comes out clean.
Notes
Storage & Make Ahead Instructions
Room Temperature: Store in an airtight container at room temperature for up to 4 days.
Freezer: Cool completely, then wrap tightly in plastic wrap and place in a freezer bag. Freeze whole or sliced for up to 3 months.
Make ahead: Assemble the batter in the loaf pan, cover, and refrigerate until ready to bake, up to 24 hrs. Add about 5 minutes to the bake time.