Combine flour, 50g sugar, salt, and yeast in a large mixing bowl.

Add warm water and melted butter to the dry ingredients, mixing until a cohesive, wet dough forms.

Perform one set of stretch-and-fold maneuvers then transfer the dough to a well-oiled 9x13 inch baking pan.

Cover and proof in a warm environment for 60 to 75 minutes until the dough has doubled in size and appears bubbly.

Preheat oven to 200°C (400°F).

Grease fingers with oil and gently dimple the surface of the dough to create deep indentations.

Fill each dimple with approximately one teaspoon of jam.

Bake for 20 minutes or until the surface is golden brown.

Combine the coating sugar and cinnamon in a small bowl.

Remove the focaccia from the oven, brush lightly with additional melted butter if desired, and immediately dust with the cinnamon-sugar mixture.

Allow to cool for 10 minutes before slicing.