Heat your oil in a frying pan over medium heat. Add the sliced onions and sauté them slowly over 30 to 40 minutes. When we say the phrase “low and slow” this is the epitome. You cannot rush this.
Stir the onions continuously until they are a golden brown and tender. Remove them from heat and allow the onions to cool completely.
Preheat your grill to 350°F to 450°F, medium heat.
In a large bowl, stir together the flour, baking powder, salt, and sugar.
Using a pastry blender, cut the butter into the mixture, until it resembles coarse crumbs.
Make a well in the center of the butter-flour mixture and add the cooled onions, havarti, milk and dill. Using a wooden spoon stir everything until the dry ingredients are just moistened.
Turn the dough out onto a lightly floured surface. Knead the dough by folding it and gently pressing, about 4 to 6 times, or just until the dough holds together. Gently pat or press the dough out into a 6-inch square that is about 1-inch thick. Use a 2-inch pastry ring, large cookie cutter or cup to cut out 12 rounds from the dough.
Plank bake the biscuits over indirect heat for 15 to 20 minutes, until they are golden brown, hot and flakey. Brush them with melted butter and serve.
Arrange the raw biscuits evenly on the soaked plank.