In an electric stand mixer with the paddle attachment, add the butter and brown sugar. Beat for around 10 minutes, ensuring to stop at the 5-minute mark to scrape the sides and bottom well.
Add the maple syrup and beat the mixture for 5-6 more minutes.
Place the butter mixture (room temperature) in a bowl, top with flaky salt and/or some more brown sugar.
Store at room temperature for a week or in the fridge for up to a month.
