30 milliliters almond liqueur (or substitute with almond extract)
Preheat oven to 350 F (175 C). Grease a 20 centimeter round springform cake pan.
Cut apples in half and slice into thin pieces. Add apple slices to a bowl and toss with lemon juice, then set aside.
In a second bowl, mix flour, baking powder, salt, and cinnamon.
In a third bowl, cream butter with sugar. Add eggs and stir to combine fully. Add almond liqueur and mix. Gradually add dry ingredients to wet and mix until just combined. Fold in 2/3 of the sliced apples. Pour batter into prepared cake pan and top with remaining apple slices. Bake 15 minutes.
Remove cake from oven and cover with tinfoil. Bake for another 45 minutes, or until toothpick inserted in the middle comes out clean.
Let cake cool for 15-20 minutes before releasing from pan and putting on a serving plate.