Preheat your oven to 350°F (180°C). Grease a 9-inch (23 cm) tart pan with removable sides or line it with parchment paper.
In a mixing bowl, combine the softened butter and sugar. Use a hand mixer or a whisk to cream the mixture until it becomes light and fluffy.
Add the egg, salt, and vanilla to the butter mixture. Mix until fully incorporated and smooth.
Gradually sift in the flour and baking powder. Use a spatula or your hands to combine until the dough comes together. The dough should be soft but not sticky.
Press the dough evenly into the prepared tart pan, covering the base and sides. Use a fork to prick the base lightly to prevent puffing during baking.
2. Prepare the Berries:
Rinse the black and red currants under cold water and remove any stems. Pat them dry with a paper towel.
In a bowl, toss the berries with 2 tablespoons of cornstarch. This step helps absorb the excess moisture and prevents the base from becoming soggy.
3. Add the Berries:
Spread the prepared currants evenly over the pastry base. Make sure the berries are evenly distributed to ensure each bite is flavorful.
4. Make the Custard Topping:
In a separate bowl, mix the sour cream and sweetened condensed milk until smooth. This creamy mixture will act as a luscious custard that sets as it bakes.
Pour the custard over the berries, ensuring that it covers the fruit evenly.
5. Bake:
Place the tart in the preheated oven and bake for 35-40 minutes, or until the custard is set and the edges of the pastry are golden brown.
To check if it’s done, insert a toothpick into the center; it should come out clean or with a few crumbs.
6. Cool and Serve:
