Ground the walnuts and soak them in rum.
Let them sit for a while (30 mins) and leave the butter out in room temperature in the meantime.
Preheat the oven to 300°F (150°C).
Line a round cake pan (10 ¼” / 26 cm) with parchment paper.
Separate egg whites from the yolks, and place them in two mixing bowls.
Using a stand electric mixer, start beating the egg whites until they become quite bubbly.
Add baking powder and stevia, and mix until stiff peaks form.
Using a hand electric mixer, mix together egg yolks, erythritol, and crumbled butter.
Add in finely ground poppy seeds and soaked walnuts.
Mix well.
When the batter is smooth, gently fold in the egg whites, using a rubber spatula.
Pour the batter into the baking pan and even it out with a spatula.
Bake for 45 to 50 minutes.
Using a toothpick, try if the crust is baked.
We use slow cooking on low temperature here so that the crust doesn’t rise too quickly and too unevenly.
When done baking, let it cool down before pouring the relatively cold filling on, otherwise the crust might fall apart.