Trim the top off the garlic, drizzle with oil and sprinkle with salt and pepper. Seal the garlic in aluminum foil, place on a baking sheet and roast until the cloves are golden and super soft, 20 to 30 minutes. Squeeze the cloves out, add a pinch of salt and smear with a knife on a flat surface to form a paste. Reserve.
Bring the stock to a simmer. Slowly add the grits in small batches, whisking the whole time. Cook, whisking often, until the grits are creamy and tender, 20 to 30 minutes.
Remove the grits from the heat and stir in the roasted garlic paste, white Cheddar and cream. Adjust the seasoning with salt and pepper. Carefully ladle the grits into the ramekins on a baking sheet. Top each ramekin with a slice of yellow Cheddar so the slice just comes over the sides of the ramekin. Bake until the cheese is gooey and bubbly, 2 to 3 minutes. Top with freshly ground black pepper and serve!