“It's all done in-house.”
You are visiting a nice new coffee shop. You tell the barista that the shop smells delicious. The barista explains that they roast their own coffee beans.
It's all done in-house.
This means a product is made in the same place where it’s sold.
The desserts are all made in-house.
Some restaurants describe food items as being “house-made,” which has a similar meaning:
It comes with your choice of two house-made dipping sauces.