Preheat the oven to 350°F. Butter an 8-inch square metal baking pan. Combine the butter, brown sugar, and golden syrup in a heavy medium saucepan.  Stir regularly over medium-low heat until the butter melts, the sugar dissolves, and the mixture is smooth. Remove from heat. Add the oats and fine salt, and stir to evenly coated. Transfer the mixture to the prepared pan, and press it out in even layer. Bake until the top is golden (the edges will be darker), about 20 to 25 minutes. Transfer the pan to a rack, and allow to cool for 5 minutes.  Then cut into 4 squares, and cut each square into 4 triangles. (The mixture will still be soft and a little crumbly; just do the best you can.) Allow to finish cooling completely in the pan. (The flapjacks will firm up as they cool.) Before serving, top with crunchy salt to taste.

*A type of syrup popular in the UK. Available at some supermarkets, specialty foods stores, and British import shops.  (If you live in Ballard, like me, you can find it at Ballard Market.)