Dense babka is almost always UNDER-proofed babka - the swirl looked ready but the dough wasn't.
The rule is visual: babka proofs open in its tin, no lid, until the dough reaches the TOP RIM. That rim moment is the cue, however long it takes - enriched doughs are slow, all that butter and sugar weighs on the yeast. Pull it early and you bake a beautiful brick. Then 180ยฐC until deep golden, and cool COMPLETELY before slicing... warm babka tears and gums, and half the "dense" verdicts online are actually just impatient knives.
Fillings: cinnamon-sugar-butter is the class version, chocolate is the other canonical one - equally traditional, equally correct. Savoury twists exist out in the world, but this enriched dough is engineered for sweet.
Next bake: same recipe, patience till the rim, ruthless cooling. Report back ๐