Seared beef rolls with lemon aioli - Irish Beef

Ingredients

• 500g Irish beef fillet, well trimmed
• 2 garlic cloves, sliced
• 1 tsp roughly cracked black peppercorns
• 2 thyme sprigs, broken up
• Olive oil, for cooking
• 1 egg, at room temperature
• 2 garlic cloves, crushed
• 2 tsp white wine vinegar
• Pinch of caster sugar
• Finely grated rind of lemon
• 1 tsp Dijon mustard
• 100 ml olive oil
• 100 ml sunflower oil
• Sea salt and freshly-ground white pepper
• Creamed horseradish
• 2 beetroots, peeled and julienned (on a mandolin is best)
• 1 bunch English radishes, julienned (on a mandolin is best)
• 100 g fresh watercress sprigs