Create Custom Border Panel?

I don't know the right way to go about this but I'd like to create a
Control like a Border Panel that can hold another element, but that
has a custom header on it that I define and can reuse.

I tried to edit the Control template of a Border but don't know its
format or if its even possible.

I want to do something along these lines:

<Style TargetType="{x:Type local:MyPanel}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type local:MyPanel}">

<!--My header xaml ...
......-->

<Border Background="Blue" Width="200" Height="200">
<element that lets junk be added into it in xaml/>
</Border>

</ControlTemplate>
</Setter.Value>
</Setter>
</Style>