How do you build a custom MCP server to give Claude fuller read/write access to QuickBooks Online?

The current QBO connector for Claude is limited: it only links one company/organization and has very limited write access alongside read access. To solve this, one member had a conversation with Claude describing the problem ('build a custom MCP server for me to do more inside QuickBooks'), and Claude walked them through the process step by step, asking clarifying questions along the way (e.g., since they were a Mac user and wanted to conserve Claude tokens, Claude suggested building the server in Python and deploying it to Google Cloud Run).