A WPF control that stacks a TextBox and a TextBlock togetther

MainWindow.xaml

<Window x:Class="YourApp.MainWindow"
                xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                xmlns:local="clr-namespace:YourApp"
                Title="MainWindow" Height="350" Width="525">

    <Grid>
        <local:TextSandwichControl Text="I'm in the textbox" 
                                   HeaderText="I'm the label"
                                   Margin="10"/>
    </Grid>
</Window>

TextSandwichControl.xaml

<UserControl x:Class="YourApp.TextSandwichControl"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             mc:Ignorable="d" 
             d:DesignWidth="200">
    <StackPanel>
        <TextBlock x:Name="HeaderTextBlock" Text="Header"/>
        <TextBox x:Name="TextTextBox" />
    </StackPanel>
</UserControl>

TextSandwichControl.xaml.cs

using System.Windows;
using System.Windows.Controls;

namespace YourApp
{
    public partial class TextSandwichControl : UserControl
    {
        public TextSandwichControl()
        {
            InitializeComponent();
        }

        public static readonly DependencyProperty HeaderTextProperty = DependencyProperty.Register(
            "HeaderText", typeof(string), typeof(TextSandwichControl), new PropertyMetadata(default(string), OnHeaderTextPropertyChanged));


        public static readonly DependencyProperty TextProperty = DependencyProperty.Register(
            "Text", typeof(string), typeof(TextSandwichControl), new PropertyMetadata(default(string), OnTextPropertyChanged));

        public string HeaderText
        {
            get => (string)GetValue(HeaderTextProperty);
            set => SetValue(HeaderTextProperty, value);
        }

        public string Text
        {
            get => (string)GetValue(TextProperty);
            set => SetValue(TextProperty, value);
        }

        private static void OnTextPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            if (d is TextSandwichControl self)
            {
                if (e.NewValue != null)
                {
                    self.TextTextBox.Text = (string)e.NewValue;
                }
            }
        }

        private static void OnHeaderTextPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            if (d is TextSandwichControl self)
            {
                if (e.NewValue != null)
                {
                    self.HeaderTextBlock.Text = (string)e.NewValue;
                }
            }
        }
    }
}