Melt a small portion of the butter in a pan over low heat and add the minced garlic. Cook it gently for about a minute, just until it turns fragrant and soft, being careful not to let it brown. Let it cool slightly before mixing it back into the rest of the softened butter.
Spoon the garlic butter onto plastic wrap and shape it into a small log. Refrigerate it until firm, which usually takes about 30 minutes. Chilled butter is key here, since it creates those flaky little pockets once it hits the oven.
In a large bowl, whisk together the flour, baking powder, and salt until fully combined. This step ensures the leavening agent is spread evenly, so your biscuits rise consistently instead of unevenly in spots.
Chop the chilled garlic butter into small pieces and work it into the flour mixture using a pastry cutter or your fingertips. Stop as soon as the mixture looks like coarse crumbs with visible butter chunks, since overmixing melts the butter too soon.
Pour the cold buttermilk into the flour mixture and stir gently with a wooden spoon. Mix only until the dry streaks disappear, because overworking the dough at this stage makes the biscuits tough instead of tender.
Turn the sticky dough onto a floured surface and pat it down gently with floured hands to about 1.5 inches thick. Avoid using a rolling pin, since patting keeps the layers loose and flaky rather than compressed.
Use a sharp biscuit cutter to punch out rounds, pressing straight down without twisting. Twisting the cutter seals the edges and can prevent the biscuits from rising evenly in the oven.
Arrange the biscuits on a parchment-lined baking sheet and brush the tops with the egg wash for a golden finish. Bake at 375°F for 18 to 20 minutes, or until the tops turn a deep golden brown.