Preheat your oven to 375°F (190°C). Prepare a muffin tray by lining it with muffin liners.

In a small pot, melt the unsalted butter over medium-high heat until it turns a light golden brown color. Continuously whisk the butter to prevent it from burning. Once browned, remove from heat and keep whisking for a short while. This residual heat will continue to brown the butter slightly.

Transfer the browned butter to a bowl and add the sugar. Stir to combine, allowing the butter to cool down slightly.

Pour in the buttermilk and whisk until well mixed. Add the egg and a splash of vanilla extract. Whisk again until the mixture is smooth.

Zest the lemon directly into the bowl and add the baking powder, baking soda, and salt. Whisk everything together until the mixture starts to thicken.

Switch to a spatula and gradually add the all-purpose flour to the bowl. Mix until there are no more streaks of flour in the batter.

Gently fold in the blueberries, being careful not to overmix. This will prevent the entire batter from turning blue.

Use a large scoop or spoon to distribute the batter evenly into the prepared muffin tray. Fill each muffin liner about 3/4 full. If there is any leftover batter, distribute it among the muffins.

Place the muffin tray in the preheated oven and bake for 15 to 20 minutes, or until the muffins turn golden brown.

Remove the muffins from the oven and let them cool in the tray for a few minutes. Then transfer them to a wire rack to cool completely.

Enjoy your delicious homemade blueberry muffins!