Step 1In the bowl of a stand mixer, or in a large bowl using a hand mixer, cream the butter, sugar and salt over low speed until combined and fluffy, about 3 minutes. With the mixer running, add the egg, beating until fully incorporated. Gradually add the flour and continue to mix until it forms a sandy texture. Form the dough into a disk and wrap in plastic wrap. Refrigerate until firm, at least 30 minutes.
Step 1In a large bowl, whisk together the sugar, eggs, heavy cream, milk and vanilla.
Step 1Butter each of 6 ramekins. Heat the oven to 375 degrees.
Step 2Cut 12 short dough circles: On a floured board, roll out the short dough to a thickness of a scant one-fourth inch. Cut the dough into 4-inch circles (wide enough to cover the base of the ramekins). You will need a total of 12 circles; re-roll and cut the dough as needed. Line the bottom of each ramekin with 1 short dough circle.
Step 3Divide the chopped croissants among the ramekins, making a solid single layer of croissants. Ladle the custard evenly over the croissants. Top each ramekin with a short dough circle.
Step 4Place the puddings on a baking sheet. Place the baking sheet in the oven and bake until the custard is puffed and set, and the crust is firm and faintly colored, about 30 minutes. Cool slightly before unmolding.
Step 5Dust the puddings with powdered sugar. The puddings can be served with whipped cream, chocolate sauce and/or fresh fruit. Serve immediately.