Spirited Strawberry Shortcake

Preheat oven to 425 degrees and butter and flour an 8-inch round cake pan.
To make the shortcake, sift together the flour, baking powder, salt, and sugar in a large bowl. Mix in the butter with your fingers, until it ranges in size from small pebbles to large grains of sand. Slowly stir in the milk a bit at a time using just enough to get the mixture to hold together.
Turn the dough onto a counter and knead it for about a minute. Press it into the cake pan, pushing it gently to the sides of the pan. Bake for 12 to 15 minutes, until the cake is lightly golden.
Let the cake cool in the pan for a few minutes before turning it onto a cooling rack. When it is still warm, but cool enough to handle, split it horizontally with a large knife. Carefully remove the top with the knife and a spatula.
About an hour before you are ready to serve the cake, gently mash the strawberries with the sugar and creme de cassis. The strawberries should be mashed enough to release some of their juices, but still maintain their shape. Set the mixture aside until you are ready to assemble the cake.
Prepare the cream mixture, by whipping the the heavy cream, sour cream, sugar, and vanilla together until it is the consistency of whipped cream.
To assemble the cake, place the bottom of the shortcake on a platter. Spoon the strawberry mixture on top, and then layer on the whipped cream. Gently place the cake top on top of the whipped cream. Slice with a sharp knife and serve immediately.