Step 1: Prepare the Sour Cream Pastry
In a food processor, pulse the cold butter and flour until the mixture resembles coarse breadcrumbs.
Add the sour cream and pulse again until the dough begins to form a ball.
Shape the dough into a flat disk, cover with cling film, and refrigerate for 20 minutes.
Roll out the dough to fit a 25cm x 2.5cm (10” x 1”) round tart tin. Prick the dough all over with a fork and chill for another 60 minutes.
Step 2: Blind Bake the Pastry
Preheat your oven to 200°C (390°F), bake mode (not fan).
Line the pastry with a double layer of foil and fill it with sugar, which acts as a weight.
Blind bake the pastry for 15 minutes, then remove the foil and sugar. Return the pastry to the oven for an additional 5 minutes, or until pale golden and dry.
While the pastry is blind baking, prepare the lemon mascarpone filling.
Step 3: Prepare the Lemon Mascarpone Filling
Reduce the oven temperature to 170°C (340°F).
In a food processor, combine the ricotta and mascarpone cheeses and blend until smooth.
Add the sugar, eggs, egg yolks, lemon rind, and lemon juice, and process again until fully incorporated.
Place the tart tin on the middle oven shelf and carefully pour the lemon mixture into the pre-baked pastry shell.
Bake for 30 minutes, or until the filling is just set but still has a slight wobble in the center.
Remove from the oven and allow the tart to cool in the tin. Then refrigerate the tart while still in the tin to allow it to fully set.
Step 4: Make the Candied Lemon Slices
In a frying pan, heat the sugar and water over medium heat until the mixture begins to turn golden brown.
Slide in the lemon slices and cook for a couple of minutes before flipping them over. Cook until the lemon slices are well coated with the toffee.
Remove the slices and place them on a sheet of baking paper to cool.
Step 5: Serve
Once the tart has set in the refrigerator, remove it from the tart tin.
Arrange the candied lemon slices on top of the tart for a beautiful garnish.