This is pretty simple. You just make a brown butter sauce. But slice your butter into pads so that it doesn’t burn. Also, unsalted butter doesn’t foam as much as salted. Use fresh sage rather than dried. It’s worth it to buy fresh herbs if you don’t grow it. Yukon’s hold their shape better, but you can use red skins etc. If you want the potatoes to brown better don’t add the onions till the end. I’ve begun frying them separate and mixing them at the end. I like my potatoes crisp and caramelized.
Melt the butter in a medium saucepan set over low-medium heat. When the butter begins to get just slightly bubbly, add a chopped garlic clove. You can chop the sage to season the butter, or as I do just place the sprigs in. Just depends on whether you prefer serving it with the sage in the product or not. It doesn’t matter. Sprigs are easier to remove if you don’t want the bits in the product. It doesn’t matter either way. Pepper and salt.
Use about a quarter cup of sage to a stick of butter. I rarely make that much at a time unless it’s for company.
To this I add my potatoes to fry. Enjoy