1. Put wine, shallots, and crushed garlic in a large pot. Set a steamer basket in pot, add clams, and cover. Bring to a boil, then simmer briskly over medium-high heat until clams open, 5 to 10 minutes.
2. Transfer clams to a plate and let cool. Strain broth from pot; set aside 3/4 cup plus 2 tbsp. and chill. Remove meat from clams, saving 8 shells; chill meat and shells.
3. Meanwhile, in a large frying pan over medium heat, sauté poblano chile, corn, and pepper in oil until chile is tender-crisp, 7 to 8 minutes. Add minced garlic; cook, stirring, 1 minute. Remove about 2 tbsp. of mixture and set aside.
4. Stir masa in a bowl with 2 tbsp. reserved clam broth and 2 tbsp. water. Stir in corn mixture from pan and half of clam meat. Spoon into 8 (4- to 6-oz.) oiled ramekins; smooth tops. Cover each with foil.
5. Put a rack in a roasting pan and fill pan with water to just below rack. Set ramekins on rack. Cover pan tightly with foil. Heat over 2 burners on high heat until a little steam escapes; reduce heat to medium-low and cook until tamales feel fairly firm, 35 minutes.
6. Meanwhile, in a small frying pan over medium-high heat, cook jalapeños until blackened, turning occasionally, 20 to 25 minutes. Let cool, then peel, seed, and dice.
7. Boil reserved 3/4 cup clam broth in a saucepan over medium-high heat until reduced to 1/3 cup, 5 minutes. Stir in jalapeños. A few minutes before serving, whisk in butter a bit at a time until melted. Stir in remaining clams and heat until warm, then stir in shells.
8. Unwrap ramekins; put on plates. Spoon clam sauce on top and set a clamshell on each. Top with reserved poblano chile, cilantro, and Fresno chiles.
*Masa for tamales has fat, leavening, and salt added to ground corn. Find it at Latino markets.
Nutritional analysis is per ramekin.