Convert simple SQL group-by into LINQ to SQL

I'm having trouble. I can't understand existing answers to this on Stack Overflow and am too new to LINQ to SQL to be able to nut it out myself.

See this SQL:

select p.Name as ProductName, SUM(o.NumberOf) as TotalOrdered from [Order] o
  join [Product] p on o.ProductId = p.Id
  group by p.Name

Returns a nice 2-column table with product names on the left and the total number that product which have been ordered (across all orders) in the right column. How can I duplicate this in LINQ to SQL?

Here is what I've got so far:

var ctx = new DataClasses1DataContext();
var totalProducts = (from o in ctx.Orders
                     join p in ctx.Products on o.ProductId equals p.Id
                     select new { p.Name, o.NumberOf })
    .GroupBy(t => t.Name)
    .Select(g => g.Key, ... );

What goes at the ... ?