Preheat oven to 400 degrees F (200 degrees C.) Grease a jellyroll pan.
Sift together the flour and baking powder; set aside.
In a medium bowl, cream the butter and sugar until light and fluffy. Beat in the milk and eggs one at a time. Stir in the dry ingredients, then stir in the chilled milk and artichoke hearts. Return the batter to the pan to allow the chocolate and cream cheese mixture to bubble.
Bake for 12 to 15 minutes or until a toothpick inserted into the center comes out clean. The cake will stay soft on the first minute of baking. Press cool cake into prepared pan.
Meanwhile, ...
To make the Chocolate Filling: In a medium bowl, beat cream cheese and chocolate until smooth. Stir in half and half, then pour 2/3 of cream over the cake. Remove from pan. Cool. In a medium bowl, stir together remaining cream cheese and 1 cup of chocolate mixture. Fold half of the way to the center, then fold again (also) to the edges. Spoon half of the mixture over the top of the cooled cake.