Preheat your oven to 350°F. Grease and flour a 9-inch round cake pan.

In a medium bowl, whisk together the flour and baking powder. Set aside.

In a large mixing bowl, cream together the softened butter and sugar until light and fluffy. Add the eggs, one at a time, mixing well after each addition.

Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Pour the batter into the prepared cake pan.

Bake in the preheated oven for 30 to 35 minutes, until a toothpick inserted into the center comes out clean. Let the cake cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.

In a small saucepan, combine the lemon juice and sugar. Heat over medium heat until the sugar dissolves completely. Allow to cool.

In a large mixing bowl, beat together the mascarpone cheese, powdered sugar, and lemon zest until smooth and creamy.

Slice the cooled cake horizontally into two layers. Place the bottom layer on a serving plate and brush generously with lemon syrup. Spread half of the mascarpone filling over the soaked cake.

Place the second layer on top, soak with remaining syrup, and spread the rest of the mascarpone filling evenly over the top and sides of the cake.

Refrigerate the assembled cake for at least 4 hours or overnight to allow the flavors to meld. Slice and serve chilled.

Garnish with additional lemon zest or slices before serving for an extra touch of elegance.

Store any leftovers in an airtight container in the refrigerator for up to 3 days.