Add the egg whites to a stand mixer with the cream of tartar and blend on high until stiff peaks form.
In another bowl or blender, mix the egg yolks and remaining wet and dry ingredients together until well blended.
Fold the egg whites a third at a time to the pumpkin mixture in the mixer until all incorporated.
Pour into a greased parchment lined 8 by 4 loaf prepared loaf pan and bake in a preheated oven for 50 minutes until golden brown. Shut oven off and keep in for 10 minutes.
Remove from loaf pan to a wire rack or cutting board, slice and enjoy warm if desired.
Store slices between parchment paper or plastic wrap in an airtight container in the fridge for up to 7 days or freeze for up to 3 months.