An example gulpfile, demonstrating minifying CSS content that is compiled from 2 LESS source files.

gulpfile.js

var concatCSS = require("gulp-concat-css"),
    gulp = require("gulp"),
    less = require("gulp-less"),
    minifyCSS = require('gulp-minify-css'),
    sourcemaps = require("gulp-sourcemaps");

gulp.task("less", function () {
    return gulp.src(["./Content/Less/Site.less", "./Content/Less/Inverted.less"])
        .pipe(sourcemaps.init())
        .pipe(less({
            paths: ["."]
        }))
        .pipe(concatCSS("Site.css"))
        .pipe(minifyCSS())
        .pipe(sourcemaps.write("../Content"))
        .pipe(gulp.dest("./Content/"));
});