Combine 1 cup flour, undissolved yeast, sugar, salt and cocoa in a large bowl. Add very warm water and butter; mix until well blended, about 1 minute.
Gradually add enough remaining flour to make a soft dough. Dough should form a ball and will be slightly sticky. Knead** on a floured surface, adding additional flour if necessary, until smooth and elastic, about 4 minutes. (If not using Pizza yeast, cover dough and allow to rest for 10 minutes.)
Pat dough with floured hands to fill greased pizza pan or baking sheet. OR roll dough on a floured counter to 12-inch circle; place in greased pizza pan or baking sheet. Form a rim by pinching the edge of the dough.
Sprinkle with dark chocolate and toffee pieces. Bake on lowest rack of oven12 to 15 minutes or until crust is lightly browned. Remove from oven.
Whisk powdered sugar, Irish cream liquor and milk to desired consistency. Drizzle over pizza; cool an additional 5 minutes before serving.
*If you don't have a thermometer, water should feel very warm to the touch.
**To knead the dough, add just enough flour to the dough and your hands to keep the dough from sticking. Flatten dough and fold it toward you.Using the heels of your hands, push the dough away with a rolling motion. Rotate dough a quarter turn and repeat the "fold, push and turn" steps. Keep kneading dough until it is smooth and elastic. Use a little more flour if dough becomes too sticky, always working the flour into the ball of dough.