CreateMaskBrush() public method

You can call this directly from start
public CreateMaskBrush ( CanvasGeometry geometry, Color color ) : System.Threading.Tasks.Task
geometry CanvasGeometry
color Color
return System.Threading.Tasks.Task
        private async void TextBlock_SizeChanged(object sender, SizeChangedEventArgs e)
        {
            var textblock = sender as TextBlock;
            utextblock = new UniversalElement(sender);

            var textformat = new CanvasTextFormat()
            {
                FontFamily = textblock.FontFamily.Source,
                FontSize = (float)textblock.FontSize,
                FontStretch = textblock.FontStretch,
                FontWeight = textblock.FontWeight
            };

            var textlayout = new CanvasTextLayout(utextblock.Masker.Device, textblock.Text, textformat, (float)textblock.ActualWidth + 6, (float)textblock.ActualHeight + 6);

            var geometry = CanvasGeometry.CreateText(textlayout);

            await utextblock.CreateMaskBrush(geometry.Stroke(3), Colors.Blue);

            var first = (utextblock.Element.Parent as Panel).Children.First();
            ElementCompositionPreview.SetElementChildVisual(first, utextblock.Visual);
        }