Combine butter, whole grain mustard, mustard powder, maple syrup, salt and black pepper in the bowl of a stand mixer fitted with a paddle attachment. Alternatively, use a hand mixer. Beat on medium low until fully combined, scraping down the bowl as needed. Taste and add more salt or pepper if desired.
If using as a spread, transfer to a bowl and use while soft. Otherwise, spoon onto parchment paper or plastic wrap and roll into a tight log. Refrigerate until firm.
