In a small saucepan boil ⅓ cup orange juice with ¾ cup raisins until almost no juice is left, about 5 minutes. Let cool completely. It can be done ahead and kept for a day at room temperature or in the fridge for a few days.
Preheat the oven to 300ºF (150°C).
Have ready a square or round 8-inch pie or cake pan with removable bottom.
In a bowl cream ¾ cup unsalted butter with a wooden spoon. Add ¼ cup sugar and combine very well.
Add raisins (with juices) and mix.
Add 1 ½ cups flour and ¼ teaspoon salt and mix thoroughly until well combined and no dry spots are visible.
Dump into the pan, and with lightly floured hands, pat evenly on the bottom.
Score with a sharp knife without reaching the bottom, and bake for 40 to 45 minutes, until it turns lightly golden and dries out.
Let cool on a wire rack and carefully unmold.
Cut along the lines, and store in an airtight container.