Position a rack in the center of the oven and preheat to 350°F. Line a muffin tin with muffin cups. In the top of a double boiler over simmering water, melt the chocolate and butter, stirring occasionally until smooth. Remove the top part of the double boiler from the bottom and cool the chocolate for about 15 minutes, or until tepid. Sift the flour, cocoa powder, baking powder, baking soda and salt into a large bowl. Stir together with a wooden spoon until thoroughly blended. In a medium bowl, whisk the eggs, sugar, and milk together. Add the chocolate and butter mixture and whisk until blended. With a rubber spatula, fold the egg mixture into the dry ingredients, folding only until the dry ingredients are moistened. Stir in the chocolate chips and walnuts. Using two spoons, fill the muffin cups 3/4 full. Bake the muffins for 16 to 18 minutes, or until springy to the touch. Cool the muffins in the pan, set on a rack. When cool, store the muffins immediately in a plastic bag or airtight container.

Preparation: 45 minutes plus baking and cooling times.