Preheat the oven to 350°F. Grease and flour a deep 8-inch round cake pan.

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

In a large mixing bowl, add the eggs. Beat on medium speed for 1 minute. Gradually add the sugar and vanilla extract. Continue beating for 7 to 8 minutes, until thick and pale.

Gently fold the dry ingredients into the egg mixture in three additions, alternating with the melted butter and milk.

Pour the batter into the prepared pan and bake for 30 to 35 minutes, until a toothpick comes out clean.

Let the cake cool in the pan for 10 minutes, then turn out onto a wire rack to cool completely.

In a clean mixing bowl, whip the heavy whipping cream until stiff peaks form. Set aside.

In another bowl, combine the mascarpone cheese, powdered sugar, lemon zest, lemon juice, and vanilla extract. Beat until smooth.

Gently fold the whipped cream into the mascarpone mixture, reserving ½ cup for the exterior of the cake.

Once cooled, slice the cake horizontally into two even layers.

Place the bottom layer on a serving plate and spread the lemon cream filling evenly over the top. Place the second layer on top.

Spread the reserved lemon cream around the sides of the cake and press the vanilla cookie crumbs into the sides.

Refrigerate the cake for at least 2 hours to set.

Just before serving, dust the top lightly with powdered sugar.