Preheat your oven to 350˚F. Line your muffin tin with paper liners.
In a medium bowl, mix melted butter, ricotta, milk, eggs, lemon zest and vanilla until smooth. In a separate bowl, mix together your dry ingredients (the flour, baking powder, salt, and sugar.)
Mix your wet ingredients and dry ingredients until just combined...careful, you don't want to overmix this here. Then, fold in your delicious, washed blueberries (or other berries) :)
Scoop your batter...
Into your lined tins.
Bake them for 18-22 minutes, or until they pass the toothpick test. I brushed mine with a little egg to make them nice and shiny.