A Walipini-type greenhouse, improved to maintain higher temperatures, have easier access to water and an additional heat source to let you grow food crops and other useful plants in the cold season in an energy-efficient way.
Underground greenhouses (also known as Walipini greenhouses) are made by digging a pit in a way that enough light would reach its bottom and covering it with a "roof" of glass or other transparent material. The plants are then grown at the bottom of the pit. This gives the benefits of thermal stability in different seasons - cool in the summer heat and relative warmth in winter. It can be used to grow crops in the cold season in latitudes that are not too far north from the equator.
I suggest the following improvements:
Using mirrors to transfer the daylight down:
Walipini greenhouses are usually made in rather shallow pits (a few feet deep). Using mirrors hung on the "walls" of the pit to transfer the daylight down would allow us to have a much deeper pit and still have enough light to grow plants in its bottom. Having a deeper pit would bring the following benefits:
Higher temperatures - at a certain depth below the surface the temperature stays constant all year round and approximately equals the mean year temperature of that location. It's hard to determine the exact depth because it depends on the precise location, its weather, and the specifics of its terrain. But approximating the data from various sources , one could expect optimal temperatures in the cold season below 10 feet.
Intersection with a geothermal heating system - deeper pit can be used for both laying geothermal pipes and making an underground greenhouse since a geothermal heating system uses the same principle - underground temperature stability to provide warmth to the living spaces in winter and cool in summer. Geothermal pipes can be laid in the bottom of the pit (between plant beds) or a bit deeper, underneath the plants. Installing geothermal pipes to fully heat the house requires quite a lot of free land space, so a part of the pit used for geothermal piping could be left uncovered to build a greenhouse in it.
The water inside the geothermal pipes absorbs heat from the soil, it is then moved upwards by a pump, heated further in the furnace until the optimal temperature, and distributed through the household heating system. Once the water gives off heat and cools down, it is moved down underground and the cycle continues.
The greenhouse part of the pit could be included in the geothermal house heating system as another "room" so that the water coming down to the pipes laid in/below the pit would be of optimal temperature to sustain a microclimate best suitable for plant growth. This can be regulated by a thermostat placed in the greenhouse.
Easier access to water - a deeper pit means a shorter distance to groundwater. One could drill one or a few small boreholes in the bottom of the pit to reach the groundwater and use a passive water acquisition system, for example, one based on capillary action or a mechanical pump to water the plants in the greenhouse. The groundwater can also be used to fill the geothermal pipes, this is known as an open loop geothermal system.
Thermally insulating the greenhouse from above:
I suggest thermally insulating the greenhouse by using two or more sheets of transparent plexiglass and leaving an air gap between them. If the greenhouse pit was deep enough, the space between the sheets would make a "second floor" where a person could fit at full height. This is convenient for cleaning the glass sheets from time to time and also, a thicker air layer means better thermal insulation. Having airtight insulation might require additional vents for CO2 and O2. Those could lead to and out of the house (to clean the air of the living spaces) or directly outside.
Another energy-efficient way to keep the temperatures optimal for plant growth inside the thermally insulated greenhouse in the cold season, apart from geothermal heating would be to use compost heating, but since the latter method is rather chaotic, it would be difficult to keep the temperatures stable and there's also a risk of fire. On the bright side - having a fire in the pit is less dangerous.