In a large mixing bowl (or the bowl of your stand mixer) cream together the butter and sugar.
1 cup butter (softened), 1 cup granulated sugar (I used unrefined)
Add in the eggs and mix until frothy.
4 large eggs (room temperature)
Add the spices (cinnamon, ginger, nutmeg, ground cloves, and all spice).
3 tsp ground cinnamon, 1/2 tsp ground ginger (optional), 1/2 tsp nutmeg (optional), 1/2 tsp all spice (optional), 1/2 tsp ground cloves (optional)
Mix in the pumpkin puree at the same time.
15 oz pumpkin puree can
Make sure everything is well blended and turn off your mixer.
Using a spatula (or a spoon) mix in the sourdough discard.
1/3 cup sourdough discard
Add the salt, bicarbonate of soda (baking soda), and baking powder.
1 tsp bicarbonate of soda (baking soda), 2 tsp baking powder, a pinch of salt (only if you use unsalted butter
Start incorporating the flour into the batter. Don't overmix.
2 cups all-purpose flour (plus 1-2 tbsp extra, if needed)
If your batter is too runny, add an extra tablespoon (or two) of flour. No more than that as you don't want a stiff batter.
Let the batter rest while preheating the oven to 350°F (176°C). This will give the batter time to activate and create a fluffy crumb.
Prepare a 9"x13" baking tray with parchment paper.
Pour the batter into the tray.
Bake at 350°F (176°C) for 35 minutes or until golden brown on top. Insert a toothpick in the centre of the cake to check if the batter is baked. The toothpick should come out clean.
Let the cake cool down while you prepare the frosting.