Preheat oven to 350°F (175°C). Grease and flour a 9x5 inch loaf pan, or line with a parchment paper sling.

In a small bowl, make the filling: stir together 1/2 cup melted butter, brown sugar, 2 tbsp cinnamon, and 1/4 tsp salt. It will form a thick, viscous paste. Set aside.

In a large bowl, whisk together the flour, 1 cup granulated sugar, baking powder, and 1/2 tsp salt.

In a medium bowl, whisk the 1/2 cup melted butter, milk, eggs, and vanilla extract.

Pour the wet ingredients into the dry ingredients. Fold with a spatula *just* until combined. Do not overmix; a few lumps are fine.

Spread half the batter into the bottom of the prepared loaf pan.

Carefully spoon the thick cinnamon filling over the batter and spread gently, avoiding the edges.

Top with the remaining batter and spread to cover the filling.

(Optional) Mix the 1 tbsp sugar and 1 tsp cinnamon and sprinkle over the top of the batter.

Bake for 50-60 minutes, or until a wooden skewer inserted in the center comes out clean (a few moist crumbs are fine, but no wet batter).

Let the bread cool in the pan on a wire rack for 20 minutes before using the parchment sling to remove it. Cool further before slicing with a serrated knife.