Mrs.Beasley poppy seed muffin

Nope, never heard about it, sorry

Nope, but I have two good recipes for lemon and poppy seed cakes, you could add walnut at your discretion and use a general baking time of 18-20 minutes

Also increasing the temp to ~400F as that's a more normal temp for this sort of thing in muffin form.

http://www.seriouseats.com/recipes/2010/02/sunday-brunch-lemon-poppy-seed-pound-cake-dessert-breakfast-recipe.html

http://smittenkitchen.com/2010/01/poppy-seed-lemon-cake/