Mix together the milk, flour, eggs, salt, butter, and sugar until well combined. I used a food processor, and I highly recommend it. Refrigerate your batter for at least an hour.
Once your batter has rested, remove it from the fridge and give it a stir. We're looking for a consistency that's slightly more runny than typical pancake batter. If your batter is too thick, add cool water (a tbsp at a time) until the desired consistency is reached. Be careful not to make the batter too watery.
If you have a crêpe pan...awesome. Get that out and heat it over medium heat. If you don't have a crêpe pan, a nonstick skillet works fine. That's what I used. :) Be sure to use a large one, about 8in.
Once your pan is hot, either spray with nonstick spray or coat in a little butter. We'll be flipping the crêpe, so we don't want it to stick.
Pour just enough batter into the pan to evenly coat the bottom. Let cook for a bit, about thirty seconds, until the batter begins to solidify.
Use a spatula or wooden spoon to loosen the crêpe from the pan, and then flip it to cook the other side. No need to get fancy and flip in the air (but if you want to, go for it! It's a lot of fun!). Using your spatula/spoon as a crutch totally works. Just make sure not to fold the wet batter onto itself.
Cook the other side until it's completely cooked, about another 30 seconds. You'll know when the crêpe is done when it's completely solid and lightly toasted but not crispy.
Once cooked, cover and set aside until you're ready to assemble the blintzes.
Once you're ready to assemble, preheat your oven to 400°F.
Lay out a crêpe, then spoon about two tbsps of your cheese filling onto the bottom half of the crêpe.
Then, fold the bottom edge closest to the filling over the filling to just cover it. (See the photos I included above for visual guidance.)
Next, fold the sides over to the center.
Finally, roll from the bottom up until you've made a little burrito shape. Place them opening-side down on a plate until all of your blintzes are made.
Heat a cast iron (what I used) or other skillet that you're able to use in the oven over medium heat. Melt butter in it to coat the bottom. Fry your blintzes on each side (start with the opening side to seal) for a couple minutes until lightly browned and crisp.
Bake your blintzes in the 400°F oven for about 10 minutes. Once they're done, transfer them to plates, spoon your blueberry topping over them, and dust with powdered sugar to serve.