Place a medium saucepan over a low heat and add the olive oil. Once heated through, add the crushed garlic, warm gently for 1 minute, stirring with a wooden spoon occasionally, taking care it doesn't catch and burn.
0.5 tsp olive oil, 1 garlic clove
Add the washed spinach leaves, stir to incorporate the garlic. Put the lid on and allow to steam in their own dampness for 1-2 minutes.
220g spinach leaves
After this time, the spinach should be wilted. Turn off the hob, drain any liquid that has come off the leaves and set aside.
Whisk the eggs and milk together. Stir the cheeses and potato slices in with the eggs. Fold in the reserved spinach with the chopped basil leaves. Season with salt and pepper to your preference.
Preheat the sandwich maker to medium heat setting. Once ready pour the egg and spinach mixture equally into pockets and close.
Your frittatas should be ready in approximately 5-6 minutes. Remove and serve immediately.
Notes
I usually buy bags of baby spinach leaves which are smaller and generally cleaner than the full size ones. You could sub other cheeses if you don't have goat's cheese.