In a medium-size bowl, combine the water, molasses, and yeast. Set aside until the yeast is dissolved and foamy. In the bowl of a stand mixer (or a large mixing bowl if making by hand), stir together the flours. Stir 1 cup of this flour mixture into the foamy yeast mixture to make a wet paste. Cover with a clean kitchen towel, and let this “sponge” rest for 30 minutes.

Add the sponge, salt, and about half of the porter to the flour mixture in the large bowl. Mix until incorporated. Stir in the walnut oil and the remaining porter as needed to form a tacky dough that barely peels itself from the bottom of the bowl. If using a stand mixer with a dough hook attachment, knead the dough until smooth and elastic, about 5 minutes (or about 10 minutes by hand). Add the aniseed during the last minute of mixing.

Turn the dough out onto a lightly floured countertop, and shape it into a rectangle. Press the walnuts on top. Fold one-third of the dough down from the top and one-third up from the bottom to encase the walnuts in a letter fold. Knead briefly, until nuts poke through the dough and air bubbles are gone. Form the dough into a ball. Place the ball in a lightly oiled bowl; cover loosely with plastic wrap. Let rise 1½ to 2 hours, until the dough is doubled in size.

Gently punch the dough down; let rest for 10 minutes. Separate the dough into two equal pieces. Press each piece into a rough rectangle about 10" long, then fold into thirds as you did to incorporate the walnuts. Press the seams in, and turn in each of the four corners for a classic batard shape. Place each loaf, fold side down, on a large baking sheet lined with parchment paper. Cover the loaves loosely with an oiled piece of plastic wrap. Let proof for 45 minutes. Heat the oven to 400ºF about 25 minutes into the proofing.

Make two or three diagonal slits across the top of each loaf with a sharp knife. Brush with water (which creates a shiny, crackly glaze on the surface). Bake for about 35 minutes total, switching their position from top to bottom about halfway through. The breads are baked through when tapping them lightly yields a hollow sound (or use a thermometer to get a reading of at least 190ºF). Let the loaves cool completely on a baking rack before slicing.