Beat the butter, then add sugar, vanilla, eggs, and molasses: Beat the butter until soft; add sugar, and beat until light and fluffy. Add vanilla and eggs, and beat until fluffy. Add molasses and beat until well-mixed.
Whisk the dry ingredients: Vigorously whisk together the dry ingredients (flour, baking soda, salt, cinnamon, ground ginger, finely ground black pepper) in a bowl.
Finish the dough: Add flour mixture to the butter/sugar/egg mixture, ⅓ at a time. Mix only until the dry ingredients become incorporated.
Press into the loaf pan and freeze: Line a 9- x 5-inch loaf pan with plastic wrap, so that some hangs over the outsides. Press the dough into the bottom of the pan. Pack it tightly, and try to make the top as level as possible. Cover the dough with the plastic overhangs. Freeze until very firm, preferably overnight.
Preheat the oven: When it comes time to bake the cookies, preheat the oven to 350°F.
Thinly slice from frozen dough: Unwrap and remove dough from the pan. Slice brick into thin slices, no more than ⅛ inch.
Bake: Working in batches, place thin slices on a parchment or a Silpat-lined sheet pan (space at least an inch apart) and bake at 350°F until the edges turn dark brown, 7-12 minutes, depending on how thinly you have sliced the dough. Check the oven for doneness at 7 minutes.
