Don't mix the cooked berries into the butter until they're room temperature. Don't put the berries in the fridge to cool because you also shouldn't add cold berries to the butter. All these steps prevents the butter from splitting. If it does split, place the bowl over a low flame to loosen the butter up and then mix vigorously until the butter comes back together.
1 tablespoon granulated sugar
1 tablespoon water
3/4 cup blueberries
1 stick (1/2 cup) unsalted butter, room temperature
1 tablespoon powdered sugar
Mix granulated sugar and water in a medium-sized saucepan. Swirl around until sugar is dissolved. Keep watching the sugar. When it just starts to caramelize (light brown), turn off the flame. Toss in blueberries and coat with the caramelized sugar. But back on a low flame, stir with a wooden spoon, and cook until blueberries just start to release their juices (1-2 minutes ). Take off the heat, pour onto a plate, and cool until room temperature.
Combine soft butter, powdered sugar, and a pinch of salt, in the bowl of an electric mixer. Mix together really well (2 minutes high speed). Scrape down the sides. Add 1/2 of the cooked blueberries. Mix really well again on high speed (at this point you're coloring the butter by mashing the cooked berries). Scrape down the sides. Mix in the other 1/2 of the blueberries until they just burst open (about 10 seconds.) Scrape blueberry butter into a ramekin. The butter tastes best served right away. But you can refrigerate it up to 5 days. And it freezes really well and stays a beautiful vibrant color.
DASH AND BELLA