WPF Large uniformGrid performance issues

Question

I'm trying to display a map using an ItemControl and an UniformGrid. The map is an observable collection of Cells. When the map is large the rendering time is very big and I'm struggling to lower it.

Here is the concerned code:

   <ItemsControl Grid.Row="1" ItemsSource="{Binding Cells}">
            <ItemsControl.ItemTemplate>
                <DataTemplate>
                    <!-- Do not use binding because it's slow -->
                    <!-- Command="{Binding Path=DataContext.CellClickedCommand, RelativeSource={RelativeSource AncestorType=ItemsControl}}" -->
                    <!-- CommandParameter="{Binding}" -->
                    <Button Name="Button" Style="{StaticResource CellButtonStyle}" Tag="{Binding}"
                            Click="Cell_OnClick"
                            MouseEnter="Cell_OnMouseEnter"
                            MouseRightButtonUp="Cell_OnMouseRightButtonUp" />

                    <DataTemplate.Triggers>
                        <DataTrigger Binding="{Binding IsIncluded}" Value="True">
                            <Setter TargetName="Button" Property="Background" Value="White" />
                        </DataTrigger>
                        <DataTrigger Binding="{Binding IsIncluded}" Value="False">
                            <Setter TargetName="Button" Property="Background" Value="Black" />
                        </DataTrigger>

                        <DataTrigger Binding="{Binding IsCurrentPlayerLocation}" Value="True">
                            <Setter TargetName="Button" Property="Foreground" Value="Green" />
                            <Setter TargetName="Button" Property="Content" Value="X" />
                            <Setter TargetName="Button" Property="BorderBrush" Value="Red" />
                            <Setter TargetName="Button" Property="BorderThickness" Value="5" />
                        </DataTrigger>
                        <DataTrigger Binding="{Binding IsCurrentPlayerLocation}" Value="False">
                            <Setter TargetName="Button" Property="Foreground" Value="Transparent" />
                            <Setter TargetName="Button" Property="Content" Value="" />
                            <Setter TargetName="Button" Property="BorderBrush" Value="DarkGray" />
                            <Setter TargetName="Button" Property="BorderThickness" Value="1" />
                        </DataTrigger>
                    </DataTemplate.Triggers>
                </DataTemplate>

            </ItemsControl.ItemTemplate>
            <ItemsControl.ItemsPanel>
                <ItemsPanelTemplate>
                    <UniformGrid HorizontalAlignment="Stretch" VerticalAlignment="Stretch"
                                 Columns="{Binding Header.ColumnCount, UpdateSourceTrigger=PropertyChanged}"
                                 Rows="{Binding Header.RowCount, UpdateSourceTrigger=PropertyChanged}" />
                </ItemsPanelTemplate>
            </ItemsControl.ItemsPanel>
        </ItemsControl>

I've tried replacing the Button with a Rectangle, it does improve the situation but it still takes > 10sec to display a 400x300 map.

Any ideas on how to make the rendering fast?