Step 1Cream butter with shortening to blend, scraping down sides of bowl often. Blend in granulated and brown sugars and salt.
Step 2Stir in eggs and vanilla. If mixture seems curdled, stir in 1/4 cup of the flour to bind.
Step 3In another bowl, stir together flour, cocoa and baking soda. Mix into batter on low speed of mixer, scraping bowl sides often. When almost mixed, stir in cream. Fold in chocolate. Chill batter 10 minutes.
Step 4Place about 1/4 cup batter per cookie on baking sheets lined with parchment paper. Flatten with wet hands, leaving 2 inches space between each cookie. Bake at 350 degrees until cookies look barely set--middles will seem slightly wet--about 12 minutes.
Step 5Let cookies cool about 10 minutes on baking sheet before removing with metal spatula. Finish cooling on rack. Store in refrigerator.