To release the flavor of poppy seeds, grind them in a food processor for 30 seconds. Martha made this recipe on episode 610 of Martha Bakes.
In a small bowl, combine water and yeast. Stir until yeast dissolves.
In the bowl of an electric mixer fitted with the dough hook, combine flour, salt, and 2 tablespoons melted butter on low speed. Add yeast mixture, and mix until well combined, about 2 minutes.
Cover bowl with plastic wrap, and let rise in a warm place until doubled in size, about 1 hour. Punch dough down, shape into a rectangle, cover in plastic wrap, and place on a baking sheet. Chill for 2 hours in the refrigerator.
Meanwhile, on a nonstick baking mat or parchment paper, roll the remaining pound of butter into an 8-inch square, between 1/8- to 1/4-inch-thick. Wrap in parchment paper, and let rest at cool room temperature, about 30 minutes.
On a lightly floured surface, roll chilled dough into a 12-inch square. Center butter square over the dough so that each side of the butter faces a corner of the dough. Fold the corners of the dough over the butter to enclose. Seal the edges by pinching together. Turn over dough, seam-side down. Roll into a 24-by-8-inch rectangle. Fold dough into thirds, aligning edges carefully and brushing off excess flour. (The object is to ensure that the butter is distributed evenly throughout so that the pastry will puff evenly when baked.) This completes one turn.
Repeat the process of rolling and folding once. Chill for 20 minutes, just until cold but not firm. Then repeat process twice, dusting work surface and dough generously with sugar, about 2 cups sugar total for the 2 turns. You will now have completed 4 turns. Refrigerate dough 20 minutes.
Meanwhile, brush 24 (3 1/2-by-1 1/2-inch) ring molds with melted butter. Transfer to 2 baking sheets lined with nonstick baking mats, and set aside.
Remove dough from refrigerator and divide in half. Sprinkle work surface and dough with half of the remaining sugar and roll out half of the dough into an 18-by-12-inch rectangle. Evenly distribute 1/2 cup of filling over the dough. (If filling with poppy seeds or nuts, you may want to sprinkle with 2 tablespoons sugar.) Roll from short side of dough creating a log. Cut crosswise into 1-inch-thick slices. Place each slice into a prepared tart ring and lightly press in place. Repeat entire process with remaining dough and filling. Cover with plastic and let rise for 40 minutes.
Meanwhile, preheat oven to 425 degrees. Bake on the middle rack until deep, golden brown, 24 to 28 minutes. Immediately remove rings using tongs and let snails cool on a wire rack.
If you don't have ring molds, you can use clean tuna cans.