Combine all-purpose flour, salt, and egg in a large mixing bowl, and pour the yeast mixture. Mix well with a spatula. Using a stand mixer with a dough hook, knead the dough for 5 minutes at high speed until smooth.
Add softened butter, and continue kneading for 5 minutes at medium-high speed until the butter has completely absorbed and the dough becomes smooth and more elastic. (If kneading by hand, you should spend less than 10 minutes to get a smooth dough.)
Cover the dough with plastic wrap and let it rise for 1 hour in a warm place until doubled in size. (Place the dough in the microwave and leave a cup of hot water aside to create a warm area to rise.)
Transfer the dough to a clean surface and gently press to release the air. Divide the dough into 18 equal pieces and round each piece into a smooth ball.
Line a 10x15-inch baking pan with parchment paper and place each bun in the pan 1 inch apart. Let the dough rise in the pan for 30 to 45 minutes in a warm area until puffy and doubled in size.
Preheat the oven to 356°F (180°C). Brush the buns with melted butter and bake for 15 minutes or until golden brown. Transfer them to a cooling rack and brush more melted butter on top while still warm.
Easy Slider Buns recipe yields cotton-soft, fluffy, buttery buns with a crispy golden brown exterior. These amazing buns are fail-proof and beginning baker friendly.