Heat garlic butter in a large skillet. Add onions and sauté until translucent.

Sprinkle with salt and pepper and squeeze in half a lemon. Add the slices of salmon and sauté on high heat for five to seven minutes on each side, until lightly brown. Transfer to a dish and let cool. 

Place drained spinach in a bowl. Add sour cream, butter, and additional salt to taste. Mix until well combined.

Roll out the pizza dough on a lightly floured pastry board until 1/8 – 1/4 inch thick. It should measure a 12- x 12-inch square. Place one slice of salmon in the top center. Spread a layer of spinach over it, and cover with the second slice of salmon. Wrap the salmon with the dough, sealing it all around, and trim any overlapping edges.

Use the remaining dough to design the top of your brioche.

Place on a lined pan and refrigerate for 30 minutes. Meanwhile, heat oven to 350 degrees Fahrenheit.

Brush dough with egg wash and add sesame seeds to your liking.

Bake for 45–50 minutes, until dough is golden brown. Let it cool a bit before serving.