Preheat oven to 350 F. Line the bottom of a 9-inch springform pan (or a pan with removable bottom) with parchment paper. You can wrap the pan with a layer of aluminum foil, in case of leaks. We are not using a water bath.
In a bowl, combine the almond flour, butter and erythritol, stir to combine. Spread the mixture on the bottom of the pan and press to make the top smooth. Bake for 10 minutes, then let it cool to room temperature.
Reduce the oven temperature to 300 F.
In a large bowl, cream together the cream cheese and sugar for 3-4 minutes, scraping down the bottom and sides of the bowl. Add vanilla, lemon juice (optional) and lemon zest (optional). Mix to combine.
Add the yogurt (or sour cream) and beat on medium speed to combine.
Slowly add the eggs, one at a time, beating with the mixer on medium speed, after each addition.
Pour the batter into the prepared pan and bake for 70-80minutes, until the edges are golden and the top is set. Let the cheesecake cool inside the oven for 40 minutes. Then take it out and let it cool completely. Refrigerate for at least 2 hours. Then you can serve it either topped with lemon curd or other sauce of your choice.
In a heat proof bowl, combine egg, egg yolks, lemon zest, juice and powdered erythritol. Whisk to combine.
Fill a large pot with water to create a double boiler. Heat over medium heat. Place the heat proof bowl above it. Whisk constantly for 8-9 minutes, until the mixture thickens. Strain through a fine mesh strainer and add the butter. Let it cool to room temperature, then cover and refrigerate.