Heat the oven to 220C/425F. Line a 33 x 46 cm / 13 x 18 inch sheet pan with parchment. Peel the beets, cut into 2 cm / 3/4-inch chunks, and toss with 1 tbsp olive oil. Spread on the sheet pan.

Roast the beets for 25 minutes, stirring once, until a fork slides in easily and the edges start to caramelize.

Let the beets cool for 5 minutes, then transfer to a food processor with the chickpeas, garlic, shallot, parsley, cilantro, cumin, coriander, salt, and pepper. Pulse 10 to 12 times until finely chopped but not pureed to a paste.

Add the chickpea flour and remaining 1 tbsp olive oil. Pulse 3 to 4 times more, just until combined. The mixture should hold together when you squeeze a spoonful in your hand.

Cover the bowl and chill the mixture for 15 minutes. This firms it up so the patties hold their shape in the oven.

Line the same sheet pan with fresh parchment and brush lightly with olive oil. Scoop the mixture into 12 portions, about 40 g each, and shape into patties roughly 2 cm / 3/4-inch thick.

Brush the tops of the patties with olive oil. Bake at 220C/425F for 20 minutes, flipping halfway through, until both sides are golden brown and firm to the touch.

While the falafel bakes, whisk the tahini, lemon juice, minced garlic, and a pinch of salt in a small bowl. Add water a tablespoon at a time until smooth and it ribbons off a spoon.

Serve the falafel warm with the tahini sauce spooned over the top or on the side for dipping.