Oi Douglas, você faz exatamente como num controlador.

class TagLibBrutaTagLib {
    def brutalidade = {attrs, body ->
         def buscaBruta = BrutalidadeMaxima.findById(attrs.id)
         out << render(template:'/brutalidade/maxima', [saida:buscaBruta])
    }
}

Pois é, fiz como explicou mas está dando erro quando vou passar nesse segundo parametro do render a variavel, simplesmente gera excessão no tomcat.

Creio eu que esse saida seria o nome que quero ter para acessar no html para acessar a variavel certo?
Eu teria de mudar algo no template para funcionar?
Qual a necessidade deste "attrs, body->" no inicio da função da taglib?

class LayoutTagLib {

	static namespace = 'layout'
	
	def menu = {attrs, body ->
		def menus = sistema.Menu.findAll()
		out << render (template: '/common/menu', [saida:menus])
	}
}

HTTP Status 500 -

type Exception report

message

description The server encountered an internal error () that prevented it from fulfilling this request.

exception

org.codehaus.groovy.grails.web.pages.exceptions.GroovyPagesException: Error applying layout : main
	java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
	java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
	java.lang.Thread.run(Thread.java:722)
root cause

org.codehaus.groovy.grails.web.pages.exceptions.GroovyPagesException: Error processing GroovyPageView: Error executing tag <layout:menu>: groovy.lang.MissingMethodException: No signature of method: ampara.LayoutTagLib.render() is applicable for argument types: (java.util.LinkedHashMap, java.util.LinkedHashMap) values: [[template:/common/menu], [saida:[ampara.sistema.Menu : 1, ...]]]
Possible solutions: menu(), every(), find()
	java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
	java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
	java.lang.Thread.run(Thread.java:722)
root cause

org.codehaus.groovy.grails.web.taglib.exceptions.GrailsTagException: Error executing tag <layout:menu>: groovy.lang.MissingMethodException: No signature of method: ampara.LayoutTagLib.render() is applicable for argument types: (java.util.LinkedHashMap, java.util.LinkedHashMap) values: [[template:/common/menu], [saida:[ampara.sistema.Menu : 1, ...]]]
Possible solutions: menu(), every(), find()
	C__Users_TI_Desktop_ampara_project_ampara_grails_app_views_layouts_main_gsp$_run_closure2.doCall(main.gsp:25)
	C__Users_TI_Desktop_ampara_project_ampara_grails_app_views_layouts_main_gsp.run(main.gsp:33)
	java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
	java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
	java.lang.Thread.run(Thread.java:722)
root cause

org.codehaus.groovy.runtime.InvokerInvocationException: groovy.lang.MissingMethodException: No signature of method: ampara.LayoutTagLib.render() is applicable for argument types: (java.util.LinkedHashMap, java.util.LinkedHashMap) values: [[template:/common/menu], [saida:[ampara.sistema.Menu : 1, ...]]]
Possible solutions: menu(), every(), find()
	C__Users_TI_Desktop_ampara_project_ampara_grails_app_views_layouts_main_gsp$_run_closure2.doCall(main.gsp:25)
	C__Users_TI_Desktop_ampara_project_ampara_grails_app_views_layouts_main_gsp.run(main.gsp:33)
	java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
	java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
	java.lang.Thread.run(Thread.java:722)
root cause

groovy.lang.MissingMethodException: No signature of method: ampara.LayoutTagLib.render() is applicable for argument types: (java.util.LinkedHashMap, java.util.LinkedHashMap) values: [[template:/common/menu], [saida:[ampara.sistema.Menu : 1, ...]]]
Possible solutions: menu(), every(), find()
	ampara.LayoutTagLib$_closure1$$ENUHUlR0.doCall(LayoutTagLib.groovy:11)
	C__Users_TI_Desktop_ampara_project_ampara_grails_app_views_layouts_main_gsp$_run_closure2.doCall(main.gsp:25)
	C__Users_TI_Desktop_ampara_project_ampara_grails_app_views_layouts_main_gsp.run(main.gsp:33)
	java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
	java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
	java.lang.Thread.run(Thread.java:722)
note The full stack trace of the root cause is available in the Apache Tomcat/7.0.25 logs.

Apache Tomcat/7.0.25

Consegui faltou colocar model: antes de [.

Vlw a todos

	def menu = {attrs, body ->
		def menus = Menu.findAll();
		def saida = "Testando"
		out << render (template: '/common/menu', model:[menus:menus])
	}