With this expansion board, you can control 2 SSRs via OneWire. Additionally, this board will provide 3 extra connectors to plug in temperature sensors.
This board can be screwed onto one SSR directly and connect to a second SSR via a grey connector. It is also possible to connect both SSRs via the grey connectors.
You could integrate this board into your fridge to only have a single cable coming out of your fridge to plug into the BrewPi Spark.