Prepare Dough: In a food processor, combine spelt flour and salt. Add chilled butter and pulse until the mixture resembles pea-sized crumbs. Gradually pour in apple cider vinegar and ice water until a shaggy dough forms. Shape into a disc, wrap in plastic, and refrigerate for at least 2 hours.

Caramelize Onions: Heat a skillet over low-medium heat and add olive oil. Cook thinly sliced onions for about 20-25 minutes until golden brown. Transfer to a bowl and let cool.

Preheat Oven: Preheat your oven to 400°F (200°C) to ensure it's ready for baking.

Roll Dough: Roll out the chilled dough into a circle about 1/4-inch thick. Place it back in the fridge for about 10 minutes.

Assemble Galette: Spread goat cheese evenly across the center of the dough. Layer caramelized onions and arrange asparagus on top.

Fold Edges: Fold the edges of the dough over the filling. Brush with egg wash and sprinkle everything but the bagel seasoning.

Bake: Bake for 45-50 minutes until the crust is golden and the filling is bubbling. Allow to cool slightly before serving.