Reduce the oven temperature to 160 degrees Celsius. In a large bowl, whisk together butter, sugar, lemon zest and vanilla extract until mixture whitens. Gradually add eggs, whisking well between each addition. Sift the flour and almond powder on top, and stir well. Add Kirsch and mix until smooth. Put the almond cream in the partially white-cooked pie stock and smooth with a spatula. Return to the oven until the almond cream is lightly browned and dry to the touch, about 20-25 minutes.