Grease very well a 7-inch cake pan and line the bottom with a circle of parchment paper.
Combine flour, baking powder, baking soda, cinnamon, nutmeg, ginger, and cloves in a medium bowl. Mix very well to blend and set aside.
In a large mixing bowl, beat the eggs and the brown sugar with an electric mixer until foamy and pale: about 3-4 minutes.
Add buttermilk, vanilla, and oil and beat again for a few seconds until smooth.
Gradually add the flour mixture, folding it gently with a rubber spatula.
In the end, add the grated carrots and the chopped walnuts. Mix gently with the spatula until absorbed.
Pour the batter into the prepared cake pan. Cover the pan with a sheet of paper towel. Wrap it tightly with aluminum foil on top but make sure the paper and the foil are loose so that the cake can rise during baking.
Place the cake pan on the Instant Pot trivet, with the handles u
Pour 3/4 cups water into the Instant Pot. Holding the handles of the trivet, place the cake pan inside the Instant Pot. Close the lid and make sure the valve is in the “Seal” position.
Select Manual setting and adjust to 40 minutes at high pressure.
When the program is over, let the pressure release naturally for 15 minutes. Release any remaining pressure manually.
Test the cake for doneness by inserting a toothpick in the center: it is ready if it comes out clean. If not, cook it for another 15 minutes at high pressure and release the pressure naturally for 10 minutes.
Let the cake cool completely before assembling it.