500g sweet potato
30g+ sage, chopped (I am obsessed with sage, so thats why the + option is there)
2 tablespoons potato flour
2 cups full cream milk (you could potentially substitute
1 teaspoon sea salt
Pepper, to taste
Freshly grated nutmeg (optional)
1. Mandolin or finely and evenly slice your vegetables. The ratio of potato to sweet potato can be messed around with - I've just written what I used. I like sweet potato but I love potato.
2. Preheat the oven to 180 degrees Celsius.
3. In a large frypan, melt the butter, and add in the sage. Cook over a medium heat not only until the sage is cooked, but the butter is a deep brown. Push it a little further than you would regular burnt butter (without completely burning it) otherwise you won't get the burnt butter taste in the final product. That said, it will still be delicious, so if you're terrified of over-burning your burnt butter, don't worry too much. Add the salt here, and the nutmeg if you're using it.
4. Once you're satisfied with the burnt-ness of your butter, turn the heat down, add the potato flour, and mix well. It will bubble up but eventually settle, and once it does, pour in the milk, one cup at a time, stirring quickly so that a roux forms. The second cup of milk will take a little while to integrate, but don't panic. Once it does (and I promise it will!) stir in the parmesan, finely and freshly grated.
5. Layer half the potatoes in a large baking tin, and follow this half of the roux. Repeat, layering the potatoes, and top with the rest of the roux. You can add some more grated cheese (Parmesan or good quality cheddar would be nice) but I wanted to minimise the amount of cheese I used, considering I eat half a block as a light snack most weeks.
6. Place into the oven for 1 hour to 1 hour and 10 minutes, checking intermittently (you may need to top it with a bit of foil if the potatoes are browning too quickly)