Trouble with the HTML() function in Golang's "html/template" package

I am having an issue with getting the "html/template" package to parse a template properly. I am trying to parse in HTML content to a template page that I have made, however, when I try, the parsed page ends up with the escaped HTML instead of the actual code I want.

The Go documentation says I can simply use the HTML() function to convert a string into a type HTML, which is known to be safe and should be parsed in as HTML. I have made my Content field in my type Page a template.HTML, which compiles just fine, but when I use the template.HTML(content) function in line 53, I get a compiler error saying:

template.HTML undefined (type *"html/template".Template has no field or method HTML)

Using HTML(content) (without the preceding template.) results in this error:

undefined: HTML

My end goal is to have other HTML files parse into index.html and be interpreted by the browser as HTML.

Any help is appreciated.

package main

import (
    "fmt"
    "html/template"
    "io"
    "io/ioutil"
    "net/http"
    "regexp"
    "strings"
)

func staticServe() {
    http.Handle(
        "/assets/",
        http.StripPrefix(
            "/assets/",
            http.FileServer(http.Dir("assets")),
        ),
    )
}

var validPath = regexp.MustCompile("^/(|maps|documents|residents|about|source)?/$")


//  This shit is messy. Clean it up.

func servePage(res http.ResponseWriter, req *http.Request) {
    type Page struct {
        Title   string
        Content template.HTML
    }

    pathCheck := validPath.FindStringSubmatch(req.URL.Path)
    path := pathCheck[1]
    fmt.Println(path)

    if path == "" {
        path = "home"
    }

    template, err := template.ParseFiles("index.html")
    if err != nil {
        fmt.Println(err)
    }

    contentByte, err := ioutil.ReadFile(path + ".html")
    if err != nil {
        fmt.Println(err)
    }
    content := string(contentByte)

    page := Page{strings.Title(path) + " - Tucker Hills Estates", template.HTML(content)}

    template.Execute(res, page)
}

//  Seriously. Goddamn.

func serveSource(res http.ResponseWriter, req *http.Request) {
    sourceByte, err := ioutil.ReadFile("server.go")
    if err != nil {
        fmt.Println(err)
    }
    source := string(sourceByte)
    io.WriteString(res, source)
}

func main() {
    go staticServe()
    http.HandleFunc("/", servePage)
    http.HandleFunc("/source/", serveSource)
    http.ListenAndServe(":9000", nil)
}