JSFiddle - React, Tailwind, and code Playground

HTML

<p>Blah<br><br><br></p>
  <p>Blah<br>Bar<br><br></p>
<p><br></p>

CSS

div {
  border: 1px solid red;
}

JavaScript

var $pp = document.getElementsByTagName("p");
for (var i = 0, $p = $pp[0], $br = [], alone = true; i < $pp.length; i = i + 1, $p = $pp[i], $br = [], alone = true) {
  for (var j = 0, $child = $p.childNodes[0]; j < $p.childNodes.length; j = j + 1, $child = $p.childNodes[j]) {
    if (($child.tagName !== "BR") && ($child.textContent.trim() !== "")) {
      alone = false;
      $br = [];
    } else {
      $br.push($child);
    }
  }
  for (var j = 0; j < $br.length - alone; j = j + 1) {
    $p.removeChild($br[j]);
  }
}