Build your levain: Place 50 g ripe, active starter, 100g rye flour, 100g whole wheat flour, and 200g room temperature filtered water in a small/medium glass mixing bowl and mix until fully combined. Lightly cover and place on the counter for 12 hours/overnight.

Check your levain for readiness. It should have risen appreciably, have a cracked appearance on top, and have small bubbles throughout the bottom and sides of the bowl. The top may not look particularly bubbly. If these signs are not present leave the levain for another 30 minutes in a warm place and check again.

If not already done, lightly crush your seeds, I use a manual spice grinder for this.

Mix your dough: Fit a stand mixer with the dough hook. To the bowl of the stand mixer, add the entire ripe levain, remaining rye flour, remaining whole wheat flour, buttermilk, golden syrup, salt, caraway seeds and anise seeds. Mix on low speed until well blended, then increase mixer speed to medium for 3-5 minutes.

Decrease speed to low again and add the butter, one pat at a time, until fully incorporated. 

Either leave your dough in the stand mixer bowl, or transfer to another container or large bowl for bulk fermentation. Lightly cover, with plastic wrap or a clean dish towel, and place in a warm area on your counter for bulk fermentation.

After one hour, do one gentle set of stretch-and-folds and return to the counter for the remainder of bulk fermentation, three more hours.

After four hours, assess your dough. It should have visibly risen in the bowl and be a little bit squishy and fluffy to the touch.

You'll need two loaf pans or Pullman pans. Grease them by using a plastic bag to spread a little butter over the inside of each loaf pan. Set aside.

Use a bowl scraper to gently turn your dough out onto a clean work surface. Use your bowl scraper or a bench scraper to divide your dough in two equal parts.

Gently shape each portion of dough into an oblong cylinder the length of your loaf pan. Turn the ends under and transfer each loaf into its pan and cover.

Leave both loaves to proof in a warm place on your counter top for 2-3 hours, until each loaf has risen to within an inch of the top of the loaf pan. It will be very soft to the touch.

Toward the end of the rise time, preheat the oven to 350 degrees Farenheit. Place the two pans side by side in the preheated oven and bake for 43-50 minutes, until the tops are golden brown, and the internal temperature of each loaf is at least 204 degrees. 

Let the loaves cool for 10 minutes in the pans then remove from pans and place on a cooling rack.

Let the loaves fully cool before slicing. Whole grain loaves take a while to fully set, so I recommend leaving them to sit for as long as 10-12 hours before slicing.