Hi Hugo,

 make sure to add correct dependencies in your __manifest__.py file 
 'depends': ['base', 'web'],

class BaseDocumentLayout(models.TransientModel):
    _inherit = 'base.document.layout'

    my_field = fields.Char('My Field')

XML File
========
        <record id="view_base_document_layout" model="ir.ui.view">
            <field name="name">Document Layout</field>
            <field name="model">base.document.layout</field>
            <field name="priority">99</field>
            <field name="inherit_id" ref="web.view_base_document_layout" />
            <field name="arch" type="xml">
                <field name="logo" position="after">
                    <field name="my_field"/>
                </field>
            </field>
      </record>

And ADD This XML File into __manifest__.py file.
Cheers!

Thanks & Regards,

Sunny Sheth