1️⃣ Make the bread: Combine lukewarm water, honey, and yeast; let sit for 5 minutes until frothy. Mix in buttermilk, salt, seeds, rye flour, and bread flour to form a dough. Knead for 8–10 minutes until smooth. Let rise in a greased bowl for 1.5 hours, then shape into a loaf and place in a greased pan. Let rise again for 45 minutes. Sprinkle oats on top (optional), bake at 375°F (190°C) for 40–50 minutes until golden and hollow-sounding when tapped. Cool completely before slicing.
2️⃣ Make the marmalade: Thinly slice oranges and lemon, removing seeds. Combine with juice and water in a pot (optional: soak overnight). Simmer for 40–50 minutes until tender. Add sugar, dissolve, and boil for 15–20 minutes until thickened, using the wrinkle test to check doneness. Skim foam, pour into sterilized jars, and seal.
3️⃣ Assemble the sandwich: Slice cooled bread and spread marmalade on each slice. Add cream cheese, brie, or nuts if desired. Serve open-faced or as a classic sandwich.