Remove outer membrane from the testicles and slice into 1-inch disks. Toss into flour, seasoned with salt and pepper, and shake of any excess. In a large oven proof skillet add canola oil and heat until it gets to the smoking point. Add garlic and onions and saute until cooked, tossing quickly so as not to burn the garlic. Remove from pan and set aside.
In the same pan with the oil residue, add the butter and place the disks of the testicles, flat side down, into the hot skillet. Cook until golden brown on both sides. Add the wine, stir in tomato paste until well incorporated, then add back the sauteed onion and garlic mixture. As the dish cooks it will thicken because of the flour dusting on the testicles. Continue to cook on top of the range for about 15 minutes, then place the pan into the preheated oven for another 30 minutes or until testicles are tender. Remove from oven and adjust seasoning. Let rest for approximately 10 minutes so flavor enhances. Garnish with chopped herbs and crispy bread.