Line the bottom of a 9 in (23 cm) round springform pan with parchment paper.In a large bowl, beat together the erythritol and butter, until fluffy.Beat in the eggs, one at a time, then the almond milk and vanilla extract.Beat in the almond flour, coconut flour, and gluten-free baking powder.Transfer 1/3 of the dough to the lined pan and smooth the top with a spatula.