How to do it...

1. Inside your command's bound function (in our case, the MyButton_Clicked function in the FChapter_10EditorModule class that's found in Chapter_10Editor.h), add the following code:

void MyButton_Clicked()
{
        
    TSharedRef<SWindow> CookbookWindow = SNew(SWindow)
        .Title(FText::FromString(TEXT("Cookbook Window")))
        .ClientSize(FVector2D(800, 400))
        .SupportsMaximize(false)
        .SupportsMinimize(false)
        [
            SNew(SVerticalBox)
            + SVerticalBox::Slot()
        .HAlign(HAlign_Center)
        .VAlign(VAlign_Center)
        [
            SNew(STextBlock)
            .Text(FText::FromString(TEXT("Hello from Slate")))
        ]
        ];

    IMainFrameModule& MainFrameModule =
        FModuleManager::LoadModuleChecked<IMainFrameModule>
        (TEXT("MainFrame"));

    if (MainFrameModule.GetParentWindow().IsValid())
    {
        FSlateApplication::Get().AddWindowAsNativeChild
        (CookbookWindow, MainFrameModule.GetParentWindow()
            .ToSharedRef());
    }
    else
    {
        FSlateApplication::Get().AddWindow(CookbookWindow);
    }
        
};

Note that we removed the ; at the end of the line stating .SupportsMinimize(false).

2. Compile your code and launch the editor.

3. When you activate the command you created, either by selecting the custom menu option or the toolbar option that you added, you should see that the window has been displayed with some centered text in the middle: