Toss garlic cloves with 15ml oil in a saucepan and cook covered on low heat for 2 minutes.
Remove garlic, cover with film, and set aside.
Season lamb and sear in a heavy pan with remaining oil over high heat for 10 minutes.
Remove lamb and garlic to a warm plate and cover with foil.
Deglaze the pan with 60ml wine or water, scraping the browned bits.
Add 200ml cream to the pan and bring to a fast boil.
Squeeze garlic from skins, mash lightly, and add to the cream sauce.
Remove from heat and stir in basil and mustard.
Slice the lamb and serve on warm plates with sautéed spinach and the garlic sauce.