Custom Content View (Widget)

How do I create a custom content view that I can insert a custom view in between? Here's a pseudo code on what I'd like to do.

SharedLayout.xaml

<ContentView>
    <StackLayout>
        <Label Text="Header"/>

        <!-- INSERT CONTENT HERE -->

        <Label Text="Footer"/>
    </StackLayout>  
</ContentView>

Usage:

<local:SharedLayout>
    <Label Text="My body inserted between Header and Footer"/>
</local:SharedLayout>

Thanks!