Wpf Expander Header issue

Hi, 

I have Expander Header Template like below: How would I assign this template to actual expander control. 

Control:

<Expander Style="{DynamicResource MultiPrinterExpanderStyle}" Grid.Row="0" x:Name="expndItem" Visibility="Visible">
                                                <Expander.Header> </Expander.Header>

</Expander>

Data Template:

  <DataTemplate x:Key="ExpanderHeaderTemplate"  DataType="{x:Type printers:PrinterDescriptor}">
        <Grid HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Width="195" Height="60" FocusVisualStyle="{x:Null}">
             <Image Grid.Column="0" Source="{DynamicResource CheckmarkImage}">

            <TextBlock Grid.Column="3"  Margin="6,0,0,0"  Text="{Binding Items[0].PrinterHeaderSecondLine}" />
        </Grid>
  </DataTemplate>

How would I apply that so it gets appear as expander header?

Thanks

Dee