class Date

Date::DATE_FORMATS[:short_ordinal] = ->(date) { date.strftime("%B #{date.day.ordinalize}") }
Date::DATE_FORMATS[:month_and_year] = '%B %Y'
# config/initializers/date_formats.rb

or Proc instance that takes a date argument as the value.
Use the format name as the hash key and either a strftime string
You can add your own formats to the Date::DATE_FORMATS hash.
== Adding your own date formats to to_fs

date.to_fs(:iso8601) # => "2007-11-10"
date.to_fs(:rfc822) # => "10 Nov 2007"
date.to_fs(:long_ordinal) # => "November 10th, 2007"
date.to_fs(:long) # => "November 10, 2007"
date.to_fs(:number) # => "20071110"
date.to_fs(:short) # => "10 Nov"

date.to_formatted_s(:db) # => "2007-11-10"
date.to_fs(:db) # => "2007-11-10"

date = Date.new(2007, 11, 10) # => Sat, 10 Nov 2007

This method is aliased to to_formatted_s.

Convert to a formatted string. See DATE_FORMATS for predefined formats.

def to_fs(format = :default)
  if formatter = DATE_FORMATS[format]
    if formatter.respond_to?(:call)
      formatter.call(self).to_s
    else
      strftime(formatter)
    end
  else
    to_default_s
  end
end