Place butter and chocolate in a microwave-safe bowl. Microwave in 30-second increments until the butter is melted. Stir well. If the chocolate isn't fully melted, return to the microwave for 15 seconds.
½ cup butter, 2 ounces unsweetened chocolate
Once the chocolate is fully melted, stir in the sugar and the vanilla.
1 cup sugar, 1 teaspoon vanilla
Allow the mixture to cool for 1-2 minutes, then stir in the eggs.
2 eggs
Add the flour and salt. Stir until combined.
1 ¼ cups flour, ¼ teaspoon salt
Spray a mini muffin tin with a nonstick spray. Use a small cookie scoop to scoop up batter and place in muffin tin.
Bake in a preheated 350°F oven for 15-17 minutes.
Allow brownie bites to cool, then remove from pan.
Store in an airtight pan at room temperature for 3-4 days.
Notes
Melt the butter and chocolate in the microwave in short increments. The chocolate will melt slower than the butter. Once the butter is melted, just let everything rest for a few minutes. The warm butter will continue to slowly melt the chocolate. Add back the microwave if needed.
Make certain the mixture isn't too hot when you add the eggs. Let it cool for 1-2 minutes after adding the sugar, stirring from time to time.
Use a small cookie scoop to place the batter into the mini muffin tin.