Preheat the oven to 425°F (220°C). Line a 9-inch springform pan with parchment paper, leaving about a 2-inch overhang around the sides; set the pan aside.
In the bowl of a stand mixer fitted with the paddle attachment, add the room-temperature cream cheese, granulated sugar, and mascarpone. Beat on high speed until smooth and fully combined, about 2 minutes, scraping the bowl down as needed.
Add the whole eggs and egg yolks to the mixer and beat just until incorporated, about 30 seconds.
Pour in the heavy cream, sour cream, vanilla extract, and lemon juice. Mix on low to medium speed until the mixture is smooth and homogenous.
Sprinkle in the cornstarch and all-purpose flour and mix briefly until just combined and no dry streaks remain.
Pour the batter into the prepared parchment-lined pan and smooth the top with a spatula.
Bake in the preheated oven for 45 minutes, until the top is deeply browned and the center is still slightly jiggly.
Turn the broiler on and broil the cheesecake for about 30 seconds, watching closely, until the top is very dark brown but not black. Remove the pan and transfer to a cooling rack to cool to room temperature.
Cover and chill the cooled cheesecake in the refrigerator for at least 8 hours, then release the springform and unmold before serving.