Preheat oven to 375°F. In a mixing bowl, combine blueberries, lemon juice, almond extract, 3 TBSP sugar, and cinnamon until blueberries are coated. Transfer to an 8x8 baking dish.
In a separate bowl, add flour, 1/2 cup sugar, salt, cubed butter, and a pinch of cinnamon. Use a pie blender, fork, or your fingers to cut the butter into the flour mix. Once small - medium pea-sized pebbles form, stir in almond slices. Spread evenly on top of the blueberries.
Bake for 35-42 minutes until the top is golden brown and the blueberries are bubbly. If it's bubbling and only slightly brown (around 30-35 minutes) you can also just turn on the broiler for 2-3 minutes until golden brown. Watch carefully so it doesn't burn if you use the broiler! Let sit for at least 20 minutes to let the juices settle.
Serve with vanilla ice cream and/or a garnish of fresh mint or basil.
Store covered either on the counter (1-2 days) or in the fridge (3-4 days). Eat leftovers at room temperature or reheat in oven for best results - this will keep the topping crisp - you can reheat in the microwave with less crisp crust results.