Preheat oven to 400°F. Craquelin is a French sugar cookie dough, topping for puff pastries to make them crispier and rounder. To prepare it, cream butter and sugar, then add flour. Roll to 1-2mm thickness between parchment paper. Freeze until ready to use. In a heavy-bottom saucepan, mix water, butter and salt. Bring to a boil slowly—so that the butter is all melted by the time the water boils. Immediately remove from heat. The butter will cling to any flour added, and you want all the flour to find some butter, so add the flour (and seasoning) all at once. Mix with a wide wooden spoon. Continue mixing on low heat for about 6 minutes, until there is a noticeable reduction in steam, or until the dough does not stick to your fingers after a good pinch. The puffs will require fewer eggs and be crispiest if you do not overcook. Transfer to a bowl and wait or mix until cool enough to add an egg. Either mix or beat in eggs 1-3, one at a time, scraping down bowl between each addition. You cannot save the dough if you add too many eggs. Lift a large dollop of dough with the spoon and let it fall slowly back into the bowl. The dough is ready when the shape under the spoon is not jagged and forms a clear V shape. Use a fork to beat the next egg in a separate bowl, and add this egg to the dough a little bit at a time, mixing and gauging whether the dough is ready each time. Stop adding egg when the dough is ready. It will be smooth and shiny. Form (or pipe) shapes 1” apart onto parchment paper on a cookie sheet (lines for eclairs, “kisses” for profiterolles or religieuses). Use a wet finger to even out any jags in the dollops. Cut and place circles of craquelin on top of each puff (about the same diameter as the puff), and strips of craquelin on top of each éclair. For mini shapes: Bake 14min at 400F then 15min at 350F. For larger shapes: Bake 20min at 400F then 15min at 350F. The puffs should be firm and light brown. Let cool on a rack.