Start by preparing your blueberry sauce if you haven't done so already. You can use store-bought sauce or make it from scratch by simmering fresh or frozen blueberries with a bit of sugar until they break down into a thick, syrupy consistency. Allow the sauce to cool completely before using it in your butter.
In a large mixing bowl, place the softened unsalted butter. Using a hand mixer or stand mixer, beat the butter on medium speed until it's light and fluffy. This should take about 2-3 minutes. The butter should be pale in color and have a creamy texture.
Once your butter is fluffy, slowly add in the cooled blueberry sauce. Mix on low speed until the sauce is fully incorporated into the butter. The mixture will take on a lovely purple hue, and the aroma will be delightful.
Now, add the milk, powdered sugar, vanilla extract, and a pinch of salt. Continue to mix on low speed until the ingredients are combined, then increase the speed to medium-high for about 1-2 minutes until everything is well blended and fluffy.
At this point, taste your Blueberry Butter. If you want it sweeter, feel free to add more powdered sugar to your liking. If the texture is too thick, you can add a touch more milk to reach your desired consistency.
Once you're satisfied with the flavor and texture, transfer the Blueberry Butter to a jar or airtight container. Chill it in the refrigerator for at least an hour to allow the flavors to meld together. Once chilled, it's ready to spread!
